How to sort a HashMap in Java [duplicate] - java

This question already has answers here:
Sort a Map<Key, Value> by values
(64 answers)
Closed 3 years ago.
How are we able to sort a HashMap<key, ArrayList>?
I want to sort on the basis of a value in the ArrayList.

Do you have to use a HashMap? If you only need the Map Interface use a TreeMap
If you want to sort by comparing values in the HashMap. You have to write code to do this, if you want to do it once you can sort the values of your HashMap:
Map<String, Person> people = new HashMap<>();
Person jim = new Person("Jim", 25);
Person scott = new Person("Scott", 28);
Person anna = new Person("Anna", 23);
people.put(jim.getName(), jim);
people.put(scott.getName(), scott);
people.put(anna.getName(), anna);
// not yet sorted
List<Person> peopleByAge = new ArrayList<>(people.values());
Collections.sort(peopleByAge, Comparator.comparing(Person::getAge));
for (Person p : peopleByAge) {
System.out.println(p.getName() + "\t" + p.getAge());
}
If you want to access this sorted list often, then you could insert your elements into a HashMap<TreeSet<Person>>, though the semantics of sets and lists are a bit different.

Sorted List by hasmap keys:
SortedSet<String> keys = new TreeSet<String>(myHashMap.keySet());
Sorted List by hashmap values:
SortedSet<String> values = new TreeSet<String>(myHashMap.values());
In case of duplicated map values:
List<String> mapValues = new ArrayList<String>(myHashMap.values());
Collections.sort(mapValues);
Good Luck!

http://snipplr.com/view/2789/sorting-map-keys-by-comparing-its-values/
get the keys
List keys = new ArrayList(yourMap.keySet());
Sort them
Collections.sort(keys)
print them.
In any case, you can't have sorted values in HashMap (according to API This class makes no guarantees as to the order of the map; in particular, it does not guarantee that the order will remain constant over time ].
Though you can push all these values to LinkedHashMap, for later use as well.

Seems like you might want a treemap.
http://docs.oracle.com/javase/7/docs/api/java/util/TreeMap.html
You can pass in a custom comparator to it if that applies.

In Java 8:
Comparator<Entry<String, Item>> valueComparator =
(e1, e2) -> e1.getValue().getField().compareTo(e2.getValue().getField());
Map<String, Item> sortedMap =
unsortedMap.entrySet().stream().
sorted(valueComparator).
collect(Collectors.toMap(Entry::getKey, Entry::getValue,
(e1, e2) -> e1, LinkedHashMap::new));
Using Guava:
Map<String, Item> map = ...;
Function<Item, Integer> getField = new Function<Item, Integer>() {
public Integer apply(Item item) {
return item.getField(); // the field to sort on
}
};
comparatorFunction = Functions.compose(getField, Functions.forMap(map));
comparator = Ordering.natural().onResultOf(comparatorFunction);
Map<String, Item> sortedMap = ImmutableSortedMap.copyOf(map, comparator);

Custom compare function which includes functionality for the Turkish alphabet or other different languages than english.
public <K extends Comparable,V extends Comparable> LinkedHashMap<K,V> sortByKeys(LinkedHashMap<K,V> map){
List<K> keys = new LinkedList<K>(map.keySet());
Collections.sort(keys, (Comparator<? super K>) new Comparator<String>() {
#Override
public int compare(String first, String second) {
Collator collator = Collator.getInstance(Locale.getDefault());
//Collator collator = Collator.getInstance(new Locale("tr", "TR"));
return collator.compare(first, second);
}
});
LinkedHashMap<K,V> sortedMap = new LinkedHashMap<K,V>();
for(K key: keys){
sortedMap.put(key, map.get(key));
}
return sortedMap;
}
here is the using example as the following
LinkedHashMap<String, Boolean> ligList = new LinkedHashMap<String, Boolean>();
ligList = sortByKeys(ligList);

Without any more information, it's hard to know exactly what you want. However, when choosing what data structure to use, you need to take into account what you need it for. Hashmaps are not designed for sorting - they are designed for easy retrieval. So in your case, you'd probably have to extract each element from the hashmap, and put them into a data structure more conducive to sorting, such as a heap or a set, and then sort them there.

If you want to combine a Map for efficient retrieval with a SortedMap, you may use the ConcurrentSkipListMap.
Of course, you need the key to be the value used for sorting.

have you considered using a LinkedHashMap<>()..?
public static void main(String[] args) {
Map<Object, Object> handler = new LinkedHashMap<Object, Object>();
handler.put("item", "Value");
handler.put(2, "Movies");
handler.put("isAlive", true);
for (Map.Entry<Object, Object> entrY : handler.entrySet())
System.out.println(entrY.getKey() + ">>" + entrY.getValue());
List<Map.Entry<String, Integer>> entries = new ArrayList<Map.Entry<String, Integer>>();
Collections.sort(entries, new Comparator<Map.Entry<String, Integer>>() {
public int compare(Map.Entry<String, Integer> a,
Map.Entry<String, Integer> b) {
return a.getValue().compareTo(b.getValue());
}
});
}
results into an organized linked object.
item>>Value
2>>Movies
isAlive>>true
check the sorting part picked from here..

I have developed a class which can be used to sort a map on the basis of keys and values. The basic idea is if you have sort a map using keys then create a TreepMap from your Map which will sort the map by keys. And in case of sorting by values create a list from entrySet and sort the list using comparator interface.
Here is the full solution :
public static void main(String[] args) {
Map<String, Integer> unSortedMap = new LinkedHashMap<String, Integer>();
unSortedMap.put("A", 2);
unSortedMap.put("V", 1);
unSortedMap.put("G", 5);
System.out.println("Unsorted Map :\n");
for (Map.Entry<String, Integer> entry : unSortedMap.entrySet()) {
System.out.println(entry.getKey() + " " + entry.getValue());
}
System.out.println("\n");
System.out.println("Sorting Map Based on Keys :\n");
Map<String, Integer> keySortedMap = new TreeMap<String, Integer>(unSortedMap);
for (Map.Entry<String, Integer> entry : keySortedMap.entrySet()) {
System.out.println(entry.getKey() + " " + entry.getValue());
}
System.out.println("\n");
System.out.println("Sorting Map Based on Values :\n");
List<Entry<String, Integer>> entryList = new ArrayList<Entry<String, Integer>>(unSortedMap.entrySet());
Collections.sort(entryList, new Comparator<Entry<String, Integer>>() {
#Override
public int compare(Entry<String, Integer> obj1, Entry<String, Integer> obj2) {
return obj1.getValue().compareTo(obj2.getValue());
}
});
unSortedMap.clear();
for (Entry<String, Integer> entry : entryList) {
unSortedMap.put(entry.getKey(), entry.getValue());
System.out.println(entry.getKey() + " " + entry.getValue());
}
}
Code is properly tested :D

Sorting HashMap by Value:
As others have pointed out. HashMaps are for easy lookups if you change that or try to sort inside the map itself you will no longer have O(1) lookup.
The code for your sorting is as follows:
class Obj implements Comparable<Obj>{
String key;
ArrayList<Integer> val;
Obj(String key, ArrayList<Integer> val)
{
this.key=key;
this.val=val;
}
public int compareTo(Obj o)
{
/* Write your sorting logic here.
this.val compared to o.val*/
return 0;
}
}
public void sortByValue(Map<String, ArrayList<>> mp){
ArrayList<Obj> arr=new ArrayList<Obj>();
for(String z:mp.keySet())//Make an object and store your map into the arrayList
{
Obj o=new Obj(z,mp.get(z));
arr.add(o);
}
System.out.println(arr);//Unsorted
Collections.sort(arr);// This sorts based on the conditions you coded in the compareTo function.
System.out.println(arr);//Sorted
}

A proper answer.
HashMap<Integer, Object> map = new HashMap<Integer, Object>();
ArrayList<Integer> sortedKeys = new ArrayList<Integer>(map.keySet());
Collections.sort(sortedKeys, new Comparator<Integer>() {
#Override
public int compare(Integer a, Integer b) {
return a.compareTo(b);
}
});
for (Integer key: sortedKeys) {
//map.get(key);
}
Note that HashMap itself cannot maintain sorting, as other answers have pointed out. It's a hash map, and hashed values are unsorted. You can thus either sort the keys when you need to and then access the values in order, as I demonstrated above, or you can find a different collection to store your data, like an ArrayList of Pairs/Tuples, such as the Pair found in Apache Commons:
https://commons.apache.org/proper/commons-lang/apidocs/org/apache/commons/lang3/tuple/Pair.html

Sorting by key:
public static void main(String[] args) {
Map<String,String> map = new HashMap<>();
map.put("b", "dd");
map.put("c", "cc");
map.put("a", "aa");
map = new TreeMap<>(map);
for (String key : map.keySet()) {
System.out.println(key+"="+map.get(key));
}
}

I developed a fully tested working solution. Hope it helps
import java.io.BufferedReader;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.List;
import java.util.StringTokenizer;
public class Main {
public static void main(String[] args) {
try {
BufferedReader in = new BufferedReader(new java.io.InputStreamReader (System.in));
String str;
HashMap<Integer, Business> hm = new HashMap<Integer, Business>();
Main m = new Main();
while ((str = in.readLine()) != null) {
StringTokenizer st = new StringTokenizer(str);
int id = Integer.parseInt(st.nextToken()); // first integer
int rating = Integer.parseInt(st.nextToken()); // second
Business a = m.new Business(id, rating);
hm.put(id, a);
List<Business> ranking = new ArrayList<Business>(hm.values());
Collections.sort(ranking, new Comparator<Business>() {
public int compare(Business i1, Business i2) {
return i2.getRating() - i1.getRating();
}
});
for (int k=0;k<ranking.size();k++) {
System.out.println((ranking.get(k).getId() + " " + (ranking.get(k)).getRating()));
}
}
in.close();
} catch (IOException e) {
e.printStackTrace();
}
}
public class Business{
Integer id;
Integer rating;
public Business(int id2, int rating2)
{
id=id2;
rating=rating2;
}
public Integer getId()
{
return id;
}
public Integer getRating()
{
return rating;
}
}
}

HashMap doesnt maintain any order, so if you want any kind of ordering, you need to store that in something else, which is a map and can have some kind of ordering, like LinkedHashMap
below is a simple program, by which you can sort by key, value, ascending ,descending ..( if you modify the compactor, you can use any kind of ordering, on keys and values)
package com.edge.collection.map;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.LinkedHashMap;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
public class SortMapByKeyValue {
Map<String, Integer> map = new HashMap<String, Integer>();
public static void main(String[] args) {
SortMapByKeyValue smkv = new SortMapByKeyValue();
smkv.createMap();
System.out.println("After sorting by key ascending order......");
smkv.sortByKey(true);
System.out.println("After sorting by key descindeng order......");
smkv.sortByKey(false);
System.out.println("After sorting by value ascending order......");
smkv.sortByValue(true);
System.out.println("After sorting by value descindeng order......");
smkv.sortByValue(false);
}
void createMap() {
map.put("B", 55);
map.put("A", 80);
map.put("D", 20);
map.put("C", 70);
map.put("AC", 70);
map.put("BC", 70);
System.out.println("Before sorting......");
printMap(map);
}
void sortByValue(boolean order) {
List<Entry<String, Integer>> list = new LinkedList<Entry<String, Integer>>(map.entrySet());
Collections.sort(list, new Comparator<Entry<String, Integer>>() {
public int compare(Entry<String, Integer> o1, Entry<String, Integer> o2) {
if (order) {
return o1.getValue().compareTo(o2.getValue());
} else {
return o2.getValue().compareTo(o1.getValue());
}
}
});
Map<String, Integer> sortedMap = new LinkedHashMap<String, Integer>();
for (Entry<String, Integer> entry : list) {
sortedMap.put(entry.getKey(), entry.getValue());
}
printMap(sortedMap);
}
void sortByKey(boolean order) {
List<Entry<String, Integer>> list = new LinkedList<Entry<String, Integer>>(map.entrySet());
Collections.sort(list, new Comparator<Entry<String, Integer>>() {
public int compare(Entry<String, Integer> o1, Entry<String, Integer> o2) {
if (order) {
return o1.getKey().compareTo(o2.getKey());
} else {
return o2.getKey().compareTo(o1.getKey());
}
}
});
Map<String, Integer> sortedMap = new LinkedHashMap<String, Integer>();
for (Entry<String, Integer> entry : list) {
sortedMap.put(entry.getKey(), entry.getValue());
}
printMap(sortedMap);
}
public void printMap(Map<String, Integer> map) {
// System.out.println(map);
for (Entry<String, Integer> entry : map.entrySet()) {
System.out.println(entry.getKey() + " : " + entry.getValue());
}
}
}
here is the git link

Convert hashmap to a ArrayList with a pair class
Hashmap<Object,Object> items = new HashMap<>();
to
List<Pair<Object,Object>> items = new ArrayList<>();
so you can sort it as you want, or list sorted by adding order.

Sorting HashMap by value in Java:
public class HashMapSortByValue {
public static void main(String[] args) {
HashMap<Long,String> unsortMap = new HashMap<Long,String>();
unsortMap.put(5l,"B");
unsortMap.put(8l,"A");
unsortMap.put(2l, "D");
unsortMap.put(7l,"C" );
System.out.println("Before sorting......");
System.out.println(unsortMap);
HashMap<Long,String> sortedMapAsc = sortByComparator(unsortMap);
System.out.println("After sorting......");
System.out.println(sortedMapAsc);
}
public static HashMap<Long,String> sortByComparator(
HashMap<Long,String> unsortMap) {
List<Map.Entry<Long,String>> list = new LinkedList<Map.Entry<Long,String>>(
unsortMap.entrySet());
Collections.sort(list, new Comparator<Map.Entry<Long,String>> () {
public int compare(Map.Entry<Long,String> o1, Map.Entry<Long,String> o2) {
return o1.getValue().compareTo(o2.getValue());
}
});
HashMap<Long,String> sortedMap = new LinkedHashMap<Long,String>();
for (Entry<Long,String> entry : list) {
sortedMap.put(entry.getKey(), entry.getValue());
}
return sortedMap;
}
}

Related

sorting hashmap with Collections.sort restarts the sort once every few values [duplicate]

This question already has answers here:
Sort a Map<Key, Value> by values
(64 answers)
Closed 3 years ago.
How are we able to sort a HashMap<key, ArrayList>?
I want to sort on the basis of a value in the ArrayList.
Do you have to use a HashMap? If you only need the Map Interface use a TreeMap
If you want to sort by comparing values in the HashMap. You have to write code to do this, if you want to do it once you can sort the values of your HashMap:
Map<String, Person> people = new HashMap<>();
Person jim = new Person("Jim", 25);
Person scott = new Person("Scott", 28);
Person anna = new Person("Anna", 23);
people.put(jim.getName(), jim);
people.put(scott.getName(), scott);
people.put(anna.getName(), anna);
// not yet sorted
List<Person> peopleByAge = new ArrayList<>(people.values());
Collections.sort(peopleByAge, Comparator.comparing(Person::getAge));
for (Person p : peopleByAge) {
System.out.println(p.getName() + "\t" + p.getAge());
}
If you want to access this sorted list often, then you could insert your elements into a HashMap<TreeSet<Person>>, though the semantics of sets and lists are a bit different.
Sorted List by hasmap keys:
SortedSet<String> keys = new TreeSet<String>(myHashMap.keySet());
Sorted List by hashmap values:
SortedSet<String> values = new TreeSet<String>(myHashMap.values());
In case of duplicated map values:
List<String> mapValues = new ArrayList<String>(myHashMap.values());
Collections.sort(mapValues);
Good Luck!
http://snipplr.com/view/2789/sorting-map-keys-by-comparing-its-values/
get the keys
List keys = new ArrayList(yourMap.keySet());
Sort them
Collections.sort(keys)
print them.
In any case, you can't have sorted values in HashMap (according to API This class makes no guarantees as to the order of the map; in particular, it does not guarantee that the order will remain constant over time ].
Though you can push all these values to LinkedHashMap, for later use as well.
Seems like you might want a treemap.
http://docs.oracle.com/javase/7/docs/api/java/util/TreeMap.html
You can pass in a custom comparator to it if that applies.
In Java 8:
Comparator<Entry<String, Item>> valueComparator =
(e1, e2) -> e1.getValue().getField().compareTo(e2.getValue().getField());
Map<String, Item> sortedMap =
unsortedMap.entrySet().stream().
sorted(valueComparator).
collect(Collectors.toMap(Entry::getKey, Entry::getValue,
(e1, e2) -> e1, LinkedHashMap::new));
Using Guava:
Map<String, Item> map = ...;
Function<Item, Integer> getField = new Function<Item, Integer>() {
public Integer apply(Item item) {
return item.getField(); // the field to sort on
}
};
comparatorFunction = Functions.compose(getField, Functions.forMap(map));
comparator = Ordering.natural().onResultOf(comparatorFunction);
Map<String, Item> sortedMap = ImmutableSortedMap.copyOf(map, comparator);
Custom compare function which includes functionality for the Turkish alphabet or other different languages than english.
public <K extends Comparable,V extends Comparable> LinkedHashMap<K,V> sortByKeys(LinkedHashMap<K,V> map){
List<K> keys = new LinkedList<K>(map.keySet());
Collections.sort(keys, (Comparator<? super K>) new Comparator<String>() {
#Override
public int compare(String first, String second) {
Collator collator = Collator.getInstance(Locale.getDefault());
//Collator collator = Collator.getInstance(new Locale("tr", "TR"));
return collator.compare(first, second);
}
});
LinkedHashMap<K,V> sortedMap = new LinkedHashMap<K,V>();
for(K key: keys){
sortedMap.put(key, map.get(key));
}
return sortedMap;
}
here is the using example as the following
LinkedHashMap<String, Boolean> ligList = new LinkedHashMap<String, Boolean>();
ligList = sortByKeys(ligList);
Without any more information, it's hard to know exactly what you want. However, when choosing what data structure to use, you need to take into account what you need it for. Hashmaps are not designed for sorting - they are designed for easy retrieval. So in your case, you'd probably have to extract each element from the hashmap, and put them into a data structure more conducive to sorting, such as a heap or a set, and then sort them there.
If you want to combine a Map for efficient retrieval with a SortedMap, you may use the ConcurrentSkipListMap.
Of course, you need the key to be the value used for sorting.
have you considered using a LinkedHashMap<>()..?
public static void main(String[] args) {
Map<Object, Object> handler = new LinkedHashMap<Object, Object>();
handler.put("item", "Value");
handler.put(2, "Movies");
handler.put("isAlive", true);
for (Map.Entry<Object, Object> entrY : handler.entrySet())
System.out.println(entrY.getKey() + ">>" + entrY.getValue());
List<Map.Entry<String, Integer>> entries = new ArrayList<Map.Entry<String, Integer>>();
Collections.sort(entries, new Comparator<Map.Entry<String, Integer>>() {
public int compare(Map.Entry<String, Integer> a,
Map.Entry<String, Integer> b) {
return a.getValue().compareTo(b.getValue());
}
});
}
results into an organized linked object.
item>>Value
2>>Movies
isAlive>>true
check the sorting part picked from here..
I have developed a class which can be used to sort a map on the basis of keys and values. The basic idea is if you have sort a map using keys then create a TreepMap from your Map which will sort the map by keys. And in case of sorting by values create a list from entrySet and sort the list using comparator interface.
Here is the full solution :
public static void main(String[] args) {
Map<String, Integer> unSortedMap = new LinkedHashMap<String, Integer>();
unSortedMap.put("A", 2);
unSortedMap.put("V", 1);
unSortedMap.put("G", 5);
System.out.println("Unsorted Map :\n");
for (Map.Entry<String, Integer> entry : unSortedMap.entrySet()) {
System.out.println(entry.getKey() + " " + entry.getValue());
}
System.out.println("\n");
System.out.println("Sorting Map Based on Keys :\n");
Map<String, Integer> keySortedMap = new TreeMap<String, Integer>(unSortedMap);
for (Map.Entry<String, Integer> entry : keySortedMap.entrySet()) {
System.out.println(entry.getKey() + " " + entry.getValue());
}
System.out.println("\n");
System.out.println("Sorting Map Based on Values :\n");
List<Entry<String, Integer>> entryList = new ArrayList<Entry<String, Integer>>(unSortedMap.entrySet());
Collections.sort(entryList, new Comparator<Entry<String, Integer>>() {
#Override
public int compare(Entry<String, Integer> obj1, Entry<String, Integer> obj2) {
return obj1.getValue().compareTo(obj2.getValue());
}
});
unSortedMap.clear();
for (Entry<String, Integer> entry : entryList) {
unSortedMap.put(entry.getKey(), entry.getValue());
System.out.println(entry.getKey() + " " + entry.getValue());
}
}
Code is properly tested :D
Sorting HashMap by Value:
As others have pointed out. HashMaps are for easy lookups if you change that or try to sort inside the map itself you will no longer have O(1) lookup.
The code for your sorting is as follows:
class Obj implements Comparable<Obj>{
String key;
ArrayList<Integer> val;
Obj(String key, ArrayList<Integer> val)
{
this.key=key;
this.val=val;
}
public int compareTo(Obj o)
{
/* Write your sorting logic here.
this.val compared to o.val*/
return 0;
}
}
public void sortByValue(Map<String, ArrayList<>> mp){
ArrayList<Obj> arr=new ArrayList<Obj>();
for(String z:mp.keySet())//Make an object and store your map into the arrayList
{
Obj o=new Obj(z,mp.get(z));
arr.add(o);
}
System.out.println(arr);//Unsorted
Collections.sort(arr);// This sorts based on the conditions you coded in the compareTo function.
System.out.println(arr);//Sorted
}
A proper answer.
HashMap<Integer, Object> map = new HashMap<Integer, Object>();
ArrayList<Integer> sortedKeys = new ArrayList<Integer>(map.keySet());
Collections.sort(sortedKeys, new Comparator<Integer>() {
#Override
public int compare(Integer a, Integer b) {
return a.compareTo(b);
}
});
for (Integer key: sortedKeys) {
//map.get(key);
}
Note that HashMap itself cannot maintain sorting, as other answers have pointed out. It's a hash map, and hashed values are unsorted. You can thus either sort the keys when you need to and then access the values in order, as I demonstrated above, or you can find a different collection to store your data, like an ArrayList of Pairs/Tuples, such as the Pair found in Apache Commons:
https://commons.apache.org/proper/commons-lang/apidocs/org/apache/commons/lang3/tuple/Pair.html
Sorting by key:
public static void main(String[] args) {
Map<String,String> map = new HashMap<>();
map.put("b", "dd");
map.put("c", "cc");
map.put("a", "aa");
map = new TreeMap<>(map);
for (String key : map.keySet()) {
System.out.println(key+"="+map.get(key));
}
}
I developed a fully tested working solution. Hope it helps
import java.io.BufferedReader;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.List;
import java.util.StringTokenizer;
public class Main {
public static void main(String[] args) {
try {
BufferedReader in = new BufferedReader(new java.io.InputStreamReader (System.in));
String str;
HashMap<Integer, Business> hm = new HashMap<Integer, Business>();
Main m = new Main();
while ((str = in.readLine()) != null) {
StringTokenizer st = new StringTokenizer(str);
int id = Integer.parseInt(st.nextToken()); // first integer
int rating = Integer.parseInt(st.nextToken()); // second
Business a = m.new Business(id, rating);
hm.put(id, a);
List<Business> ranking = new ArrayList<Business>(hm.values());
Collections.sort(ranking, new Comparator<Business>() {
public int compare(Business i1, Business i2) {
return i2.getRating() - i1.getRating();
}
});
for (int k=0;k<ranking.size();k++) {
System.out.println((ranking.get(k).getId() + " " + (ranking.get(k)).getRating()));
}
}
in.close();
} catch (IOException e) {
e.printStackTrace();
}
}
public class Business{
Integer id;
Integer rating;
public Business(int id2, int rating2)
{
id=id2;
rating=rating2;
}
public Integer getId()
{
return id;
}
public Integer getRating()
{
return rating;
}
}
}
HashMap doesnt maintain any order, so if you want any kind of ordering, you need to store that in something else, which is a map and can have some kind of ordering, like LinkedHashMap
below is a simple program, by which you can sort by key, value, ascending ,descending ..( if you modify the compactor, you can use any kind of ordering, on keys and values)
package com.edge.collection.map;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.LinkedHashMap;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
public class SortMapByKeyValue {
Map<String, Integer> map = new HashMap<String, Integer>();
public static void main(String[] args) {
SortMapByKeyValue smkv = new SortMapByKeyValue();
smkv.createMap();
System.out.println("After sorting by key ascending order......");
smkv.sortByKey(true);
System.out.println("After sorting by key descindeng order......");
smkv.sortByKey(false);
System.out.println("After sorting by value ascending order......");
smkv.sortByValue(true);
System.out.println("After sorting by value descindeng order......");
smkv.sortByValue(false);
}
void createMap() {
map.put("B", 55);
map.put("A", 80);
map.put("D", 20);
map.put("C", 70);
map.put("AC", 70);
map.put("BC", 70);
System.out.println("Before sorting......");
printMap(map);
}
void sortByValue(boolean order) {
List<Entry<String, Integer>> list = new LinkedList<Entry<String, Integer>>(map.entrySet());
Collections.sort(list, new Comparator<Entry<String, Integer>>() {
public int compare(Entry<String, Integer> o1, Entry<String, Integer> o2) {
if (order) {
return o1.getValue().compareTo(o2.getValue());
} else {
return o2.getValue().compareTo(o1.getValue());
}
}
});
Map<String, Integer> sortedMap = new LinkedHashMap<String, Integer>();
for (Entry<String, Integer> entry : list) {
sortedMap.put(entry.getKey(), entry.getValue());
}
printMap(sortedMap);
}
void sortByKey(boolean order) {
List<Entry<String, Integer>> list = new LinkedList<Entry<String, Integer>>(map.entrySet());
Collections.sort(list, new Comparator<Entry<String, Integer>>() {
public int compare(Entry<String, Integer> o1, Entry<String, Integer> o2) {
if (order) {
return o1.getKey().compareTo(o2.getKey());
} else {
return o2.getKey().compareTo(o1.getKey());
}
}
});
Map<String, Integer> sortedMap = new LinkedHashMap<String, Integer>();
for (Entry<String, Integer> entry : list) {
sortedMap.put(entry.getKey(), entry.getValue());
}
printMap(sortedMap);
}
public void printMap(Map<String, Integer> map) {
// System.out.println(map);
for (Entry<String, Integer> entry : map.entrySet()) {
System.out.println(entry.getKey() + " : " + entry.getValue());
}
}
}
here is the git link
Convert hashmap to a ArrayList with a pair class
Hashmap<Object,Object> items = new HashMap<>();
to
List<Pair<Object,Object>> items = new ArrayList<>();
so you can sort it as you want, or list sorted by adding order.
Sorting HashMap by value in Java:
public class HashMapSortByValue {
public static void main(String[] args) {
HashMap<Long,String> unsortMap = new HashMap<Long,String>();
unsortMap.put(5l,"B");
unsortMap.put(8l,"A");
unsortMap.put(2l, "D");
unsortMap.put(7l,"C" );
System.out.println("Before sorting......");
System.out.println(unsortMap);
HashMap<Long,String> sortedMapAsc = sortByComparator(unsortMap);
System.out.println("After sorting......");
System.out.println(sortedMapAsc);
}
public static HashMap<Long,String> sortByComparator(
HashMap<Long,String> unsortMap) {
List<Map.Entry<Long,String>> list = new LinkedList<Map.Entry<Long,String>>(
unsortMap.entrySet());
Collections.sort(list, new Comparator<Map.Entry<Long,String>> () {
public int compare(Map.Entry<Long,String> o1, Map.Entry<Long,String> o2) {
return o1.getValue().compareTo(o2.getValue());
}
});
HashMap<Long,String> sortedMap = new LinkedHashMap<Long,String>();
for (Entry<Long,String> entry : list) {
sortedMap.put(entry.getKey(), entry.getValue());
}
return sortedMap;
}
}

Creating a leaderboard in Java using primitive arrays [duplicate]

This question already has answers here:
Sort a parallel array using Arrays.sort()
(5 answers)
Closed 4 years ago.
I'm creating a console game in Java. And I want to keep track of the scores and names.
I've already created two arrays.
String[] PlayerNames = {"Bob", "Rick", "Jack"}; // just an example
int[] PlayerScores = {40, 20, 60}; // just an example
I want to sort their scores, but also know who the score belongs to, and then print it out like this:
Jack 60
Bob 40
Rick 20
Create a map with the player names as the keys and the scores as the values, then sort the map based on the values:
public static void main(String[] args) {
Map<String, Integer> unsortedMap = new HashMap<String, Integer>();
unsortedMap.put("Jack", 60);
unsortedMap.put("Bob", 40);
unsortedMap.put("Rick", 20);
Map<String, Integer> sortedMap = sortByValue(unsortedMap);
printMap(sortedMap);
}
private static Map<String, Integer> sortByValue(Map<String, Integer> unsortMap) {
// 1. Convert Map to List of Map
List<Map.Entry<String, Integer>> list =
new LinkedList<Map.Entry<String, Integer>>(unsortMap.entrySet());
// 2. Sort list with Collections.sort(), provide a custom Comparator
// Try switch the o1 o2 position for a different order
Collections.sort(list, new Comparator<Map.Entry<String, Integer>>() {
public int compare(Map.Entry<String, Integer> o1,
Map.Entry<String, Integer> o2) {
return (o1.getValue()).compareTo(o2.getValue());
}
});
// 3. Loop the sorted list and put it into a new insertion order Map LinkedHashMap
Map<String, Integer> sortedMap = new LinkedHashMap<String, Integer>();
for (Map.Entry<String, Integer> entry : list) {
sortedMap.put(entry.getKey(), entry.getValue());
}
/*
//classic iterator example
for (Iterator<Map.Entry<String, Integer>> it = list.iterator(); it.hasNext(); ) {
Map.Entry<String, Integer> entry = it.next();
sortedMap.put(entry.getKey(), entry.getValue());
}*/
return sortedMap;
}
public static <K, V> void printMap(Map<K, V> map) {
for (Map.Entry<K, V> entry : map.entrySet()) {
System.out.println("Key : " + entry.getKey()
+ " Value : " + entry.getValue());
}
}
Note: see https://www.mkyong.com/java/how-to-sort-a-map-in-java/ for more details.
You can use a hashmap for this. Use each name from playerNames as a key and create a list for the values (in case two or more players with the same name get a score). A hashmap allows only one value per key, which is why you should create a list of integers for the scores.
Map<String, List<Integer>> scoreboard = new HashMap<>();

Sort map using comparator not working properly

I'm having a map(this comes directly from the web service, so the input is map anyways) and I'm trying to sort the map based on description. But, two keys are having empty description and they are required anyhow now. When I sort one key goes on missing and one key with empty description is available. Here is my code
public class TestArabic {
public static void main(String[] args) {
Map<Integer, NationalityDto> m = new HashMap<Integer, NationalityDto>();
NationalityDto n10 = new NationalityDto();
n10.setNatid(110);
n10.setDesc("");
m.put(110, n10);
NationalityDto n2 = new NationalityDto();
n2.setNatid(102);
n2.setDesc("الهند");
m.put(102, n2);
NationalityDto n3 = new NationalityDto();
n3.setNatid(103);
n3.setDesc("سعودي");
m.put(103, n3);
NationalityDto n1 = new NationalityDto();
n1.setNatid(101);
n1.setDesc("مصر");
m.put(101, n1);
NationalityDto n4 = new NationalityDto();
n4.setNatid(104);
n4.setDesc("الكويت");
m.put(104, n4);
NationalityDto n5 = new NationalityDto();
n5.setNatid(105);
n5.setDesc("لبنان");
m.put(105, n5);
NationalityDto n6 = new NationalityDto();
n6.setNatid(106);
n6.setDesc("");
m.put(106, n6);
System.out.println("Actual map");
System.out.println(m);
Map<Integer, NationalityDto> sortedMap = sortByValue(m);
System.out.println("About to sort the map");
System.out.println(sortedMap);
List<NationalityDto> list = new ArrayList<>();
//Add elements
for(Map.Entry<Integer, NationalityDto> m1 : sortedMap.entrySet()) {
list.add(m1.getValue());
}
Collections.sort(list, (e1, e2) -> e1.getDesc().compareTo(e2.getDesc()));
Map<Integer, NationalityDto> map = new LinkedHashMap<>();
for(NationalityDto dto : list){
map.put(dto.getNatid(), dto);
}
System.out.println("Sorted map");
System.out.println(map);
}
private static Map<Integer, NationalityDto> sortByValue(Map m) {
Map<Integer, NationalityDto> sortedMap = new TreeMap(new ValueComparator(m));
sortedMap.putAll(m);
return sortedMap;
}
}
class ValueComparator implements Comparator<Integer> {
Map<Integer, NationalityDto> map;
public ValueComparator(Map map) {
this.map = map;
}
public int compare(Integer s1, Integer s2) {
// TODO Auto-generated method stub
return ((NationalityDto) map.get(s1)).getDesc().compareTo(((NationalityDto) map.get(s2)).getDesc());
}
}
Output
{101=NationalityDto [natid=101, desc=مصر], 102=NationalityDto [natid=102, desc=الهند], 103=NationalityDto [natid=103, desc=سعودي], 104=NationalityDto [natid=104, desc=الكويت], 105=NationalityDto [natid=105, desc=لبنان], 106=NationalityDto [natid=106, desc=], 110=NationalityDto [natid=110, desc=]}
About to sort the map
{106=NationalityDto [natid=110, desc=], 104=NationalityDto [natid=104, desc=الكويت], 102=NationalityDto [natid=102, desc=الهند], 103=NationalityDto [natid=103, desc=سعودي], 105=NationalityDto [natid=105, desc=لبنان], 101=NationalityDto [natid=101, desc=مصر]}
Sorted map
{110=NationalityDto [natid=110, desc=], 104=NationalityDto [natid=104, desc=الكويت], 102=NationalityDto [natid=102, desc=الهند], 103=NationalityDto [natid=103, desc=سعودي], 105=NationalityDto [natid=105, desc=لبنان], 101=NationalityDto [natid=101, desc=مصر]}
Now 106 key is missing.
You cannot sort a TreeMap by value. Anyone who told you you could was wrong, and the value comparator you have used is broken.
The only valid way of sorting a map by value is the one you've used in your main method: sort the entries as a list and dump into a LinkedHashMap.
for(Map.Entry<Integer, NationalityDto> m1 : sortedMap.entrySet()) {
list.add(m1.getValue());
}
Collections.sort(list, (e1, e2) -> e1.getDesc().compareTo(e2.getDesc()));
Map<Integer, NationalityDto> map = new LinkedHashMap<>();
for(NationalityDto dto : list){
map.put(dto.getNatid(), dto);
This part will sort the entries if you don't give it a broken map in the first place. Your sortByValue method is broken; don't use it.

Finding the Key from Value in Map

So I am having a bit of trouble understanding how to do this. I am building a word counter in Java using Map<String, Integer> where a word is the String and the amount of times that word was said in a .txt document is Integer. This is all working great...but I am trying to develop a part where it will display at the bottom what the top 5 results are ---> what the top 5 map.values() are.
The problem I have run into is after I find the value, I can't get the String with it.
Any suggestions would be very helpful to me.
You need to use the Map.Entry<String, Integer> to get the pair of the key and value.
The values() method returns only values, whereas the keySet() method returns only the keys.
Firstly, you should sort your map, based on values, to get the top five results.
The straightforward approach uses a Comparator. See the answer here for more.
Then you simply get the first five entries of the map.getEntrySet(). It would be easier to use an Iterator for this.
UPDATE:
Set<Entry<String, Integer>> set = wordCount.entrySet();
List<Entry<String, Integer>> list = new ArrayList<Entry<String, Integer>>(set);
Collections.sort(list, new Comparator<Map.Entry<String, Integer>>() {
public int compare(Map.Entry<String, Integer> o1, Map.Entry<String, Integer> o2) {
return o2.getValue().compareTo(o1.getValue());
}
});
int topResults = 5;
Iterator<Entry<String, Integer>> iter = list.iterator(); //refer the sorted collection
while (iter.hasNext() && topResults > 0 ) {
Map.Entry<String, Integer> entry = iter.next();
System.out.println(entry.getKey() + "->" + entry.getValue());
topResults --;
}
a) Iterate over the map, this way you have both keys and values accessible:
for (Map.Entry<String, Object> entry : map.entrySet()) {
String key = entry.getKey();
Integer value = entry.getValue();
// ...
}
b) build a second map for reverse lookup, e.g. Map - note that this is likely not a good idea here as you may have duplicate keys (same number for different words)
c) consider using a bidimap - this is a map which you can query both by key and by value.
I suggest you to override Comparator and build your Map constructor based on it.
Code is showed below:
class ValueComparator implements Comparator {
Map map;
public ValueComparator(Map map) {
this.map = map;
}
public int compare(Object keyA, Object keyB) {
Comparable valueA = (Comparable) map.get(keyA);
Comparable valueB = (Comparable) map.get(keyB);
return valueB.compareTo(valueA);
}
}
public class YourClass{
public static void main(String[] args) {
HashMap<String, Integer> map = new HashMap<String, Integer>();
map.put("a", 10);
map.put("b", 30);
map.put("c", 50);
map.put("d", 40);
map.put("e", 20);
System.out.println(map);
Map sortedMap = sortByValue(map);
System.out.println(sortedMap);
}
public static Map sortByValue(Map unsortedMap) {
Map sortedMap = new TreeMap(new ValueComparator(unsortedMap));
sortedMap.putAll(unsortedMap);
return sortedMap;
}
}

Sort a map on key and value

I want to sort a Map on key and value. First on key then on value.
For example, this should be the result;
1,2
1,3
2,1
2,2
Anyone has a suggestion on how to achieve this effectively? I've been seeing people using a TreeMap to sort keys, however i also need values.
Or ofcouse any other method of sorting pairs on key and value is welcome.
import java.util.SortedSet;
import java.util.TreeSet;
public class SortMapOnKeyAndValue {
public static void main(String[] args) {
SortedSet<KeyValuePair> sortedSet = new TreeSet<KeyValuePair>();
sortedSet.add(new KeyValuePair(1, 2));
sortedSet.add(new KeyValuePair(2, 2));
sortedSet.add(new KeyValuePair(1, 3));
sortedSet.add(new KeyValuePair(2, 1));
for (KeyValuePair keyValuePair : sortedSet) {
System.out.println(keyValuePair.key+","+keyValuePair.value);
}
}
}
class KeyValuePair implements Comparable<KeyValuePair>{
int key, value;
public KeyValuePair(int key, int value) {
super();
this.key = key;
this.value = value;
}
public int compareTo(KeyValuePair o) {
return key==o.key?value-o.value:key-o.key;
}
}
What you are looking for a is SortedSetMultimap, part of Google's Guava library. The implementation they include is named TreeMultimap:
http://docs.guava-libraries.googlecode.com/git-history/release/javadoc/com/google/common/collect/TreeMultimap.html
If you're not familiar with it, Guava is a fantastic library with lots of great stuff that you sometimes think should be in the standard Java libraries. I think Java 8, actually, will include some stuff from Guava (at least that seemed to me to be the drift of this item: http://openjdk.java.net/jeps/108).
Sounds like you want a multi map of some type e.g.
SortedMap<Key, SortedSet<Value>> map = new TreeMap<Key, SortedSet<Value>>();
map.put(1, new TreeSet<Integer>(Arrays.asList(1, 2)));
map.put(2, new TreeSet<Integer>(Arrays.asList(2, 1)));
System.out.println(map);
prints
{ 1 = {1, 2}, 2 = {1, 2}}
The other answers have indicated the problem with duplicate keys, but I am guessing you have pairs that you want to sort and the Map bit was just a mistake. The cleanest solution I can think of is to create a custom Pair class which implements Comparator and compares both the key and the value of two Pairs. You can then use Collections.sort to sort this.
If you are willing to take the risk, you could use the constructor that allows you to specify a Comparator: http://download.oracle.com/javase/1.5.0/docs/api/java/util/TreeMap.html#TreeMap%28java.util.Comparator%29
Having said that, what you want to do is ugly as hell and illegal because:
* the order will not be consistent with equals(), which is a requisite for SortedSet)
* the order may change due to altering values in the Map, and I don't know if its implementation allows for this.
I think that you need something else. Perhaps you would be better by creating an object that has both key and value and properly implements equals(), hashcode() and Comparable, and use a SortedSet with it.
EDIT: I have answered the generic question (sort a map on key and value) without looking at your samples. As others have written, you cannot have duplicate keys in a map.
It is not possible, because a map cannot contain duplicate keys. A TreeMap is always sorted by key value (assuming, the key type is Comparable).
But for those task we usually take a map whose values are lists:
Map<Integer, List<Integer>> map = new TreeMap<Integer, List<Integer>>();
// add some values in random order
List<Integer> list = new ArrayList<Integer>();
list.add(2);
list.add(1);
map.put(2,list);
list = new ArrayList<Integer>();
list.add(2);
list.add(1);
map.put(1,list);
// result
for (Integer key:map.keySet()) { // map is already sorted
List<Integer> value = map.get(key);
Collections.sort(value); // list of values needs sorting
for (Integer innerValue:value) {
System.out.printf("%s : %s%n", key, innerValue);
}
}
The overall idea is, convert the Map into List, sort the List and put the sorted list back to a Map.
Map ---> List ---> Sort ---> Map
Example
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
public class SortMyMap{
public static void main(String[] args) {
System.out.println("Unsort Map......");
Map<String,String> unsortMap = new HashMap<String,String>();
unsortMap.put("1", "1");
unsortMap.put("2", "A");
unsortMap.put("3", "2");
Iterator iterator=unsortMap.entrySet().iterator();
for (Map.Entry entry : unsortMap.entrySet()) {
System.out.println("Key : " + entry.getKey()
+ " Value : " + entry.getValue());
}
System.out.println("Sorted Map......");
Map<String,String> sortedMap = sortByComparator(unsortMap);
for (Map.Entry entry : sortedMap.entrySet()) {
System.out.println("Key : " + entry.getKey()
+ " Value : " + entry.getValue());
}
}
private static Map sortByComparator(Map unsortMap) {
List list = new LinkedList(unsortMap.entrySet());
//sort list based on comparator
Collections.sort(list, new Comparator() {
public int compare(Object o1, Object o2) {
return ((Comparable) ((Map.Entry) (o1)).getValue())
.compareTo(((Map.Entry) (o2)).getValue());
}
});
//put sorted list into map again
Map sortedMap = new LinkedHashMap();
for (Iterator it = list.iterator(); it.hasNext();) {
Map.Entry entry = (Map.Entry)it.next();
sortedMap.put(entry.getKey(), entry.getValue());
}
return sortedMap;
}
}
Please follow this code :-
This code will first sort the map by Key and then by value.
Just write a main method and call this method as follow :-
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
public class SortMapByKeyAndValue
{
public static void main(String[] args)
{
aMapSortProgramByKeyAndValue();
}
private static void aMapSortProgramByKeyAndValue()
{
Map<String, Integer> myMap = new HashMap<String, Integer>();
// putting values in the Map
myMap.put("Jayant", 80);
myMap.put("Abhishek", 90);
myMap.put("Anushka", 80);
myMap.put("Amit", 75);
myMap.put("Spandan", 50);
myMap.put("Hari", 55);
myMap.put("Keshav", 60);
System.out.println("Map data without Sort :-");
for (Entry<String, Integer> myEntryMapData : myMap.entrySet())
{
System.out.println("The Map data is Key: " + myEntryMapData.getKey() + " Value: "
+ myEntryMapData.getValue());
}
List<Entry<String, Integer>> myMapDataAsList = new ArrayList<Map.Entry<String, Integer>>();
myMapDataAsList.addAll(myMap.entrySet());
System.out.println("Map data Stored in List, The whole List is : " + myMapDataAsList);
Iterator<Entry<String, Integer>> myListIterator = myMapDataAsList.iterator();
System.out.println("Map data Stored in List, Print through iterator :-");
for (; myListIterator.hasNext();)
{
Entry<String, Integer> myListData = myListIterator.next();
System.out.println("The List data is Key: " + myListData.getKey() + " Value: " + myListData.getValue());
}
Collections.sort(myMapDataAsList, new Comparator<Entry<String, Integer>>()
{
#Override
public int compare(Entry<String, Integer> dataOne, Entry<String, Integer> dataTwo)
{
return dataOne.getKey().compareTo(dataTwo.getKey());
}
});
System.out.println("After Sort by the Key the Map data is : ");
myListIterator = myMapDataAsList.iterator();
for (; myListIterator.hasNext();)
{
Entry<String, Integer> myListData = myListIterator.next();
System.out.println("The List data is Key: " + myListData.getKey() + " Value: " + myListData.getValue());
}
Collections.sort(myMapDataAsList, new Comparator<Entry<String, Integer>>()
{
#Override
public int compare(Entry<String, Integer> dataOne, Entry<String, Integer> dataTwo)
{
return dataOne.getValue().compareTo(dataTwo.getValue());
}
});
System.out.println("After Sort by the vale the Map data is : ");
myListIterator = myMapDataAsList.iterator();
for (; myListIterator.hasNext();)
{
Entry<String, Integer> myListData = myListIterator.next();
System.out.println("The List data is Key: " + myListData.getKey() + " Value: " + myListData.getValue());
}
}
}
you can't have such map
1->11
1->21
the key '1' is common so 21 will replace 11

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