I'll keep this simple:
I have an ArrayList of names, I have to remove certain words that contain a specific letter, but I am having trouble restarting the for-loop. This is what I got:
public static void someRandomFunction(){
List<String> arrList = new ArrayList<>(Arrays.asList("Hello",
"Everyone",
"I'm",
"Struggling",
"In",
"Computer",
"Science"));
System.out.println("Start of List: " + wordList + "\n");
System.out.println("\nDrop: \"a\"");
someRandomFunction(wordList, "a");
System.out.println("wordList is now: " + wordList);
}
public static List<String> removeIfContains(List<String> strList, String removeIf){
List<String> tempList = new ArrayList<>(strList); // creating a copy
for(int i = 0; i < tempList.size(); i++){
if(tempList.get(i).contains(removeIf))
tempList.remove(i);
}
//Return will not work because of incompatible types.
}
An example of what the compiled code should be:
ArrayList [ Hello, Everyone, I'm, Am, Struggling, In, Computer, Science]
Remove words that start with "A":
New ArrayList [Hello, Everyone, I'm, Struggling, In, Computer, Science]
Remove words that start with "I":
New ArrayList [Hello, Everyone, Am, Struggling, Computer, Science]
The problem with my code is that it won't return the wordlist to how it was before as it begins to read the new word it needs to drop.
If you just want to remove each element in an ArrayList that starts with a certain letter you can utilize the removeIf() method which:
Removes all of the elements of this collection that satisfy the given predicate.
wrodList.removeIf(e -> e.contains(thisLetter));
(Java 8+ required)
It sounds like you want the list to reset after each time you remove elements. To do this you can create a copy ArrayList to check against, and then after each time, set it back to the original:
List<String> copy = new ArrayList<>(wordList); //Creates a copy of wordList
I believe this is what you are looking for. I'm not sure if you want a an instance or static method. I believe your issue is that you are not creating a copy. I noted where I was creating a copy. Good luck in CS.. we've all struggled at one point.
public static void someRandomFunction(){
List<String> arrList = new ArrayList<>(Arrays.asList("Hello",
"Everyone",
"I'm",
"Struggling",
"In",
"Computer",
"Science"));
System.out.println(removeIfContains(arrList, "H")); // calling the function and passing the list and what
System.out.println(removeIfContains(arrList, "I")); // I want to remove from the list
}
public static List<String> removeIfContains(List<String> strList, String removeIf){
List<String> tempList = new ArrayList<>(strList); // creating a copy
for(int i = 0; i < tempList.size(); i++){
if(tempList.get(i).contains(removeIf))
tempList.remove(i);
}
return tempList; // returning the copy
}
Related
Lets say you have an array like this: String[] theWords = {"hello", "good bye", "tomorrow"}. I want to remove/ignore all the strings in the array that have the letter 'e'. How would I go about doing that? My thinking is to go:
for (int arrPos = 0; arrPos < theWords.length; arrPos++) { //Go through the array
for (int charPos = 0; charPos < theWords[arrPos].length(); charPos++) { //Go through the strings in the array
if (!((theWords[arrPos].charAt(charPos) == 'e')) { //Finds 'e' in the strings
//Put the words that don't have any 'e' into a new array;
//This is where I'm stuck
}
}
}
I'm not sure if my logic works and if I'm even on the right track. Any responses would be helpful. Many thanks.
One easy way to filter an array is to populate an ArrayList with if in a for-each loop:
List<String> noEs = new ArrayList<>();
for (String word : theWords) {
if (!word.contains("e")) {
noEs.add(word);
}
}
Another way in Java 8 is to use Collection#removeIf:
List<String> noEs = new ArrayList<>(Arrays.asList(theWords));
noEs.removeIf(word -> word.contains("e"));
Or use Stream#filter:
String[] noEs = Arrays.stream(theWords)
.filter(word -> !word.contains("e"))
.toArray(String[]::new);
You can directly use contains() method of String class to check if "e" is present in your string. That will save your extra for loop.
It would be simple if you use ArrayList.
importing import java.util.ArrayList;
ArrayList<String> theWords = new ArrayList<String>();
ArrayList<String> yourNewArray = new ArrayList<String>;//Initializing you new array
theWords.add("hello");
theWords.add("good bye");
theWords.add("tommorow");
for (int arrPos = 0; arrPos < theWords.size(); arrPos++) { //Go through the array
if(!theWords.get(arrPos).contains("e")){
yourNewArray.add(theWords.get(arrPos));// Adding non-e containing string into your new array
}
}
The problem you have is that you need to declare and instantiate the String array before you even know how many elements are going to be in it (since you wouldn't know how many strings would not contain 'e' before going through the loop).
Instead, if you use an ArrayList you do not need to know the required size beforehand. Here is my code from start to end.
String[] theWords = { "hello", "good bye", "tomorrow" };
//creating a new ArrayList object
ArrayList<String> myList = new ArrayList<String>();
//adding the corresponding array contents to the list.
//myList and theWords point to different locations in the memory.
for(String str : theWords) {
myList.add(str);
}
//create a new list containing the items you want to remove
ArrayList<String> removeFromList = new ArrayList<>();
for(String str : myList) {
if(str.contains("e")) {
removeFromList.add(str);
}
}
//now remove those items from the list
myList.removeAll(removeFromList);
//create a new Array based on the size of the list when the strings containing e is removed
//theWords now refers to this new Array.
theWords = new String[myList.size()];
//convert the list to the array
myList.toArray(theWords);
//now theWords array contains only the string(s) not containing 'e'
System.out.println(Arrays.toString(theWords));
I am fairly new to Java and I have stumbled across a problem I cannot figure out for the life of me. First let me explain what I am trying to do then I will show you the code I have so far.
I have a webservice that returns an array of arrays(which include company and lines of business strings). I wish to transform this into a string list, which I did in the first line of code below. Then I wish to Iterate through the list and every I come across a different value for company, I want to create a new ArrayList and add the associated line of business to the new list. Example output of webservice: 80,80,64,64 (this is presorted so the same companies will always be grouped together) the associated lobs would be 1,2,3,4 respectively. What I want: arraylist[0]: 1,2 arrayList[1]: 3,4
What I have so far:
List coList = Arrays.asList(coArray);
//create list of lists
List<List<String>> listOfLists = new ArrayList<List<String>>();
String cmp = "";
for (int i=0;i<coList.size();i++){//loop over coList and find diff in companies
String currentCo = ((__LOBList)coList.get(i)).getCompany();
String currentLob = ((__LOBList)coList.get(i)).getLobNum();
if(i<coArray.length-1){
String nextCo = ((__LOBList)coList.get(i+1)).getCompany();
if((currentCo.equals(nextCo))){
//do nothing companies are equal
}else{
log("NOT EQUAL"); //insert logic to create a new array??
ArrayList<String> newList = new ArrayList<String>();
// for(int j=0;j<coList.size();j++){
newList.add( ((__LOBList)coList.get(i)).getLobNum());
// }
for(int k=0; k<listOfLists.size();k++){//loop over all lists
for(int l=0;l<listOfLists.get(k).size();l++){ //get first list and loop through
}
listOfLists.add(newList);
}
}
}
}
My problem here is that it is not adding the elements to the new string array. It does correctly loop through coList and I put a log where the companies are not equal so I do know where I need to create a new arrayList but I cannot get it to work for the life of me, please help!
Yes you can do this but it's really annoying to write in Java. Note: This is a brain dead simple in a functional programming language like Clojure or Haskell. It's simply a function called group-by. In java, here's how I'd do this:
Initialize a List of Lists.
Create a last pointer that is a List. This holds the last list you've added to.
Iterate the raw data and populate into the last as long as "nothing's changed". If something has changed, create a new last.
I'll show you how:
package com.sandbox;
import java.util.ArrayList;
import java.util.List;
public class Sandbox {
public static void main(String[] args) {
ArrayList<String> rawInput = new ArrayList<String>();
rawInput.add("80");
rawInput.add("80");
rawInput.add("60");
rawInput.add("60");
new Sandbox().groupBy(rawInput);
}
public void groupBy(List<String> rawInput) {
List<List<String>> output = new ArrayList<>();
List<String> last = null;
for (String field : rawInput) {
if (last == null || !last.get(0).equals(field)) {
last = new ArrayList<String>();
last.add(field);
output.add(last);
} else {
last.add(field);
}
}
for (List<String> strings : output) {
System.out.println(strings);
}
}
}
This outputs:
[80, 80]
[60, 60]
Of course, you can do what the other guys are suggesting but this changes your data type. They're suggesting "the right tool for the job", but they're not mentioning guava's Multimap. This will make your life way easier if you decide to change your data type to a map.
Here's an example of how to use it from this article:
public class MutliMapTest {
public static void main(String... args) {
Multimap<String, String> myMultimap = ArrayListMultimap.create();
// Adding some key/value
myMultimap.put("Fruits", "Bannana");
myMultimap.put("Fruits", "Apple");
myMultimap.put("Fruits", "Pear");
myMultimap.put("Vegetables", "Carrot");
// Getting the size
int size = myMultimap.size();
System.out.println(size); // 4
// Getting values
Collection<string> fruits = myMultimap.get("Fruits");
System.out.println(fruits); // [Bannana, Apple, Pear]
Collection<string> vegetables = myMultimap.get("Vegetables");
System.out.println(vegetables); // [Carrot]
// Iterating over entire Mutlimap
for(String value : myMultimap.values()) {
System.out.println(value);
}
// Removing a single value
myMultimap.remove("Fruits","Pear");
System.out.println(myMultimap.get("Fruits")); // [Bannana, Pear]
// Remove all values for a key
myMultimap.removeAll("Fruits");
System.out.println(myMultimap.get("Fruits")); // [] (Empty Collection!)
}
}
It sounds to me like a better choice would be a Map of Lists. Let the company ID be the key in the Map and append each new item for that company ID to the List that's the value.
Use the right tool for the job. Arrays are too low level.
Create a Map<String, List<Bussiness>>
Each time you retrieve a company name, first check if the key is already in the map. If it is, retrieve the list and add the Bussiness object to it. If it is not, insert the new value when a empty List and insert the value being evaluated.
try to use foreach instead of for
just like
foreach(List firstGroup in listOfLists)
foreach(String s in firstGroup)
............
Thanks for the input everyone!
I ended up going with a list of lists:
import java.util.*;
import search.LOBList;
public class arraySearch {
/**
* #param args
*/
public static void main(String[] args) {
LOBList test = new LOBList();
test.setCompany("80");
test.setLOB("106");
LOBList test1 = new LOBList();
test1.setCompany("80");
test1.setLOB("601");
LOBList test2 = new LOBList();
test2.setCompany("80");
test2.setLOB("602");
LOBList test3 = new LOBList();
test3.setCompany("90");
test3.setLOB("102");
LOBList test4 = new LOBList();
test4.setCompany("90");
test4.setLOB("102");
LOBList test5 = new LOBList();
test5.setCompany("100");
test5.setLOB("102");
LOBList BREAK = new LOBList();
BREAK.setCompany("BREAK");
BREAK.setLOB("BREAK");
BREAK.setcompany_lob("BREAK");
// create arraylist
ArrayList<LOBList> arlst=new ArrayList<LOBList>();
// populate the list
arlst.add(0,test);
arlst.add(1,test1);
arlst.add(2,test2);
arlst.add(3,test3);
arlst.add(4,test4);
arlst.add(5,test5);
//declare variables
int idx = 0;
String nextVal = "";
//loops through list returned from service, inserts 'BREAK' between different groups of companies
for(idx=0;idx<arlst.size();idx++){
String current = arlst.get(idx).getCompany();
if(idx != arlst.size()-1){
String next = arlst.get(idx+1).getCompany();
nextVal = next;
if(!(current.equals(next))){
arlst.add(idx+1,BREAK);
idx++;
}
}
}
//add last break at end of arrayList
arlst.add(arlst.size(),BREAK);
for(int i=0;i<arlst.size();i++){
System.out.println("co:" + arlst.get(i).getCompany());
}
//master array list
ArrayList<ArrayList<LOBList>> mymasterList=new ArrayList<ArrayList<LOBList>>();
mymasterList = searchListCreateNewLists(arlst);
//print log, prints all elements in all arrays
for(int i=0;i<mymasterList.size();i++){
for(int j=0;j<mymasterList.get(i).size();j++){
System.out.println("search method: " + mymasterList.get(i).get(j).getCompany());
}
System.out.println("end of current list");
}
}
//method to loop over company array, finds break, creates new array list for each company group,
//adds this to a list of lists(masterList)
public static ArrayList<ArrayList<LOBList>> searchListCreateNewLists(ArrayList<LOBList> list){
ArrayList<ArrayList<LOBList>> masterList=new ArrayList<ArrayList<LOBList>>();
int end = 0;
int start = 0;
int index = 0;
for(int i=0;i<list.size();i++){
if(list.get(i).getCompany().equals("BREAK")){
end = i;//end is current index
masterList.add(new ArrayList<LOBList>());
for(int j = start;j<end;j++){
masterList.get(index).add(list.get(j));
}
index++;
start = i+1;
}
}
return masterList;
}
}
The output is:
search method: 80
search method: 80
search method: 80
end of current list
search method: 90
search method: 90
end of current list
search method: 100
end of current list
So all company LOBList objects with Company: 80, are grouped together in a list, as are 90 and 100.
To iterate through the list you can use
ListIterator litr = coList.listIterator();
while(litr.hasNext()){
}
I have to count the number of unique words from a text document using Java. First I had to get rid of the punctuation in all of the words. I used the Scanner class to scan each word in the document and put in an String ArrayList.
So, the next step is where I'm having the problem! How do I create a method that can count the number of unique Strings in the array?
For example, if the array contains apple, bob, apple, jim, bob; the number of unique values in this array is 3.
public countWords() {
try {
Scanner scan = new Scanner(in);
while (scan.hasNext()) {
String words = scan.next();
if (words.contains(".")) {
words.replace(".", "");
}
if (words.contains("!")) {
words.replace("!", "");
}
if (words.contains(":")) {
words.replace(":", "");
}
if (words.contains(",")) {
words.replace(",", "");
}
if (words.contains("'")) {
words.replace("?", "");
}
if (words.contains("-")) {
words.replace("-", "");
}
if (words.contains("‘")) {
words.replace("‘", "");
}
wordStore.add(words.toLowerCase());
}
} catch (FileNotFoundException e) {
System.out.println("File Not Found");
}
System.out.println("The total number of words is: " + wordStore.size());
}
Are you allowed to use Set? If so, you HashSet may solve your problem. HashSet doesn't accept duplicates.
HashSet noDupSet = new HashSet();
noDupSet.add(yourString);
noDupSet.size();
size() method returns number of unique words.
If you have to really use ArrayList only, then one way to achieve may be,
1) Create a temp ArrayList
2) Iterate original list and retrieve element
3) If tempArrayList doesn't contain element, add element to tempArrayList
Starting from Java 8 you can use Stream:
After you add the elements in your ArrayList:
long n = wordStore.stream().distinct().count();
It converts your ArrayList to a stream and then it counts only the distinct elements.
I would advice to use HashSet. This automatically filters the duplicate when calling add method.
Although I believe a set is the easiest solution, you can still use your original solution and just add an if statement to check if value already exists in the list before you do your add.
if( !wordstore.contains( words.toLowerCase() )
wordStore.add(words.toLowerCase());
Then the number of words in your list is the total number of unique words (ie: wordStore.size() )
This general purpose solution takes advantage of the fact that the Set abstract data type does not allow duplicates. The Set.add() method is specifically useful in that it returns a boolean flag indicating the success of the 'add' operation. A HashMap is used to track the occurrence of each original element. This algorithm can be adapted for variations of this type of problem. This solution produces O(n) performance..
public static void main(String args[])
{
String[] strArray = {"abc", "def", "mno", "xyz", "pqr", "xyz", "def"};
System.out.printf("RAW: %s ; PROCESSED: %s \n",Arrays.toString(strArray), duplicates(strArray).toString());
}
public static HashMap<String, Integer> duplicates(String arr[])
{
HashSet<String> distinctKeySet = new HashSet<String>();
HashMap<String, Integer> keyCountMap = new HashMap<String, Integer>();
for(int i = 0; i < arr.length; i++)
{
if(distinctKeySet.add(arr[i]))
keyCountMap.put(arr[i], 1); // unique value or first occurrence
else
keyCountMap.put(arr[i], (Integer)(keyCountMap.get(arr[i])) + 1);
}
return keyCountMap;
}
RESULTS:
RAW: [abc, def, mno, xyz, pqr, xyz, def] ; PROCESSED: {pqr=1, abc=1, def=2, xyz=2, mno=1}
You can create a HashTable or HashMap as well. Keys would be your input strings and Value would be the number of times that string occurs in your input array. O(N) time and space.
Solution 2:
Sort the input list.
Similar strings would be next to each other.
Compare list(i) to list(i+1) and count the number of duplicates.
In shorthand way you can do it as follows...
ArrayList<String> duplicateList = new ArrayList<String>();
duplicateList.add("one");
duplicateList.add("two");
duplicateList.add("one");
duplicateList.add("three");
System.out.println(duplicateList); // prints [one, two, one, three]
HashSet<String> uniqueSet = new HashSet<String>();
uniqueSet.addAll(duplicateList);
System.out.println(uniqueSet); // prints [two, one, three]
duplicateList.clear();
System.out.println(duplicateList);// prints []
duplicateList.addAll(uniqueSet);
System.out.println(duplicateList);// prints [two, one, three]
public class UniqueinArrayList {
public static void main(String[] args) {
StringBuffer sb=new StringBuffer();
List al=new ArrayList();
al.add("Stack");
al.add("Stack");
al.add("over");
al.add("over");
al.add("flow");
al.add("flow");
System.out.println(al);
Set s=new LinkedHashSet(al);
System.out.println(s);
Iterator itr=s.iterator();
while(itr.hasNext()){
sb.append(itr.next()+" ");
}
System.out.println(sb.toString().trim());
}
}
3 distinct possible solutions:
Use HashSet as suggested above.
Create a temporary ArrayList and store only unique element like below:
public static int getUniqueElement(List<String> data) {
List<String> newList = new ArrayList<>();
for (String eachWord : data)
if (!newList.contains(eachWord))
newList.add(eachWord);
return newList.size();
}
Java 8 solution
long count = data.stream().distinct().count();
In my application I need to have a 2 dimensional array. If I define it fix it works fine, like this:
static final String arrGroupelements[] = {"India", "Australia", "England", "South Africa"};
static final String arrChildelements[][] = { {"Sachin Tendulkar", "Raina", "Dhoni", "Yuvi" },
{"Ponting", "Adam Gilchrist", "Michael Clarke"},
{"Andrew Strauss", "kevin Peterson", "Nasser Hussain"},
{"Graeme Smith", "AB de villiers", "Jacques Kallis"} };
However, in my code I have two lists. the first is list of recipe name that i can get it.
LinkedList<String> recipeList = dbShoppingHandler.getAllRecipeNames();
String arrGroupelements[] = new String[recipeList.size()];
for(int i=0; i<recipeList.size(); i++) {
arrGroupelements[i] = recipeList.get(i);
}
My second list is list of ingredients. In order to get list of ingredients i need to set recipe name and then i can get the list. However, i don't know how put this list as second dimension. my code is like this:
String arrChildelements[][] = new String[recipeList.size()][20];
for(int i=0; i<recipeList.size(); i++) {
LinkedList<String> ingredient = dbShoppingHandler.getIngredientsOfRecipeName(recipeList.get(i));
for(int j=0; j<ingredient.size(); j++) {
arrChildelements[i][j] = ingredient.get(j);
}
}
Bad thing is, i need to set a number (in my case 20) for second dimension. If i do like this for lists that have 5 items i will have 15 " " elements and those have more than 20 items the code ignore them.
First dimension is fix but i need to adjust second dimension based on number of ingredients.
any suggestion are appreciated. thanks.
How about assigning an array in the desired sise:
String arrChildelements[][] = new String[recipeList.size()][];
// not mentioning second dimension size ^^
for(int i=0; i<recipeList.size(); i++) {
LinkedList<String> ingredient = dbShoppingHandler.getIngredientsOfRecipeName(recipeList.get(i));
arrChildelements[i] = String[ingredient.size()];
// assigning new array here ^^
for(int j=0; j<ingredient.size(); j++) {
arrChildelements[i][j] = ingredient.get(j);
}
}
I suggest not to use 2D arrays for dynamic structures. Arrays are immutable, so you have to copy them, create gaps and move elements around. The standard Java library doesn't offer many useful methods to do that.
Instead, use a list of lists:
List<List<String>> data = new ArrayList<List<String>>();
Lists have many useful methods to append elements, insert and remove them and they will make you life much easier.
The simplest way to to not assume you know the length in advance.
String[][] arrChildelements[] = new String[recipeList.size()][];
for(int i=0; i<recipeList.size(); i++) {
List<String> ingredient = dbShoppingHandler.getIngredientsOfRecipeName(recipeList.get(i));
arrChildelements[i] = ingredient.toArray(new String[0]);
}
I am a beginner to java, and need some help.
I am trying to convert an Abstract Data type Foo which is an associated list to an Arraylist of the strings B. How do you loop through the list and add each string to the array.
I may be over thinking it, but I am lost now.
Thanks for the help in advance.
Instantiate a new ArrayList:
List<String> myList = new ArrayList<String>();
Iterate over your data structure (with a for loop, for instance, more details on your code would help.) and for each element (yourElement):
myList.add(yourElement);
If you have an arraylist of String called 'foo', you can easily append (add) it to another ArrayList, 'list', using the following method:
ArrayList<String> list = new ArrayList<String>();
list.addAll(foo);
that way you don't even need to loop through anything.
You should be able to do something like:
ArrayList<String> list = new ArrayList<String>();
for( String s : foo )
{
list.add(s);
}
Array list can be implemented by the following code:
Arraylist<String> list = new ArrayList<String>();
list.add(value1);
list.add(value2);
list.add(value3);
list.add(value4);
Well, you have to iterate through your abstract type Foo and that depends on the methods available on that object. You don't have to loop through the ArrayList because this object grows automatically in Java. (Don't confuse it with an array in other programming languages)
Recommended reading.
Lists in the Java Tutorial
thanks for the help, I've solved my problem :) Here is the code if anyone else needs it :D
import java.util.*;
public class HelloWorld {
public static void main(String[] Args) {
Map<Integer,List<Integer>> map = new HashMap<Integer,List<Integer>>();
List<Integer> list = new ArrayList<Integer>();
list.add(1);
list.add(9);
list.add(11);
map.put(1,list);
int First = list.get(1);
int Second = list.get(2);
if (First < Second) {
System.out.println("One or more of your items have been restocked. The current stock is: " + First);
Random rn = new Random();
int answer = rn.nextInt(99) + 1;
System.out.println("You are buying " + answer + " New stock");
First = First + answer;
list.set(1, First);
System.out.println("There are now " + First + " in stock");
}
}
}
If you're using Java 9, there's an easy way with less number of lines without needing to initialize or add method.
List<String> list = List.of("first", "second", "third");