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Sorting arrays from lowest to highest numbers with ratios using methods in Java

I am writing a program that takes in the number of ingredients. The prog
This is my code:
import java.util.Scanner;
public class Restaurant {
public static void main(String[] args) {
Scanner scan = new Scanner(System.in);
int count = scan.nextInt();
}

Change this sortCalories function to the one below. Also you need to pass price array as second parameter like this sortCalories(calories,price, ingredientName);:
public static void sortCalories(double[] calories,double[] price, String[] ingredientName) {
double temp;
String temp1;
for (int p=0; p<calories.length; p++) {
for (int j=p+1; j<calories.length; j++) {
if(calories[p]/price[p]>calories[j]/price[j]) {
temp = calories[p];
calories[p] = calories[j];
calories[j] = temp;
temp = price[p];
price[p] = price[j];
price[j] = temp;
temp1 = ingredientName[p];
ingredientName[p] = ingredientName[j];
ingredientName[j] = temp1;
}
}
}
}

Altering the value of k in kNN algorithm - Java

I have applied the KNN algorithm for classifying handwritten digits. the digits are in vector format initially 8*8, and stretched to form a vector 1*64..
As it stands my code applies the kNN algorithm but only using k = 1. I'm not entirely sure how to alter the value k after attempting a couple of things I kept getting thrown errors. If anyone could help push me in the right direction it would be really appreciated. The training dataset can be found here and the validation set here.
ImageMatrix.java
import java.util.*;
public class ImageMatrix {
private int[] data;
private int classCode;
private int curData;
public ImageMatrix(int[] data, int classCode) {
assert data.length == 64; //maximum array length of 64
this.data = data;
this.classCode = classCode;
}
public String toString() {
return "Class Code: " + classCode + " Data :" + Arrays.toString(data) + "\n"; //outputs readable
}
public int[] getData() {
return data;
}
public int getClassCode() {
return classCode;
}
public int getCurData() {
return curData;
}
}
ImageMatrixDB.java
import java.util.*;
import java.io.*;
import java.util.ArrayList;
public class ImageMatrixDB implements Iterable<ImageMatrix> {
private List<ImageMatrix> list = new ArrayList<ImageMatrix>();
public ImageMatrixDB load(String f) throws IOException {
try (
FileReader fr = new FileReader(f);
BufferedReader br = new BufferedReader(fr)) {
String line = null;
while((line = br.readLine()) != null) {
int lastComma = line.lastIndexOf(',');
int classCode = Integer.parseInt(line.substring(1 + lastComma));
int[] data = Arrays.stream(line.substring(0, lastComma).split(","))
.mapToInt(Integer::parseInt)
.toArray();
ImageMatrix matrix = new ImageMatrix(data, classCode); // Classcode->100% when 0 -> 0% when 1 - 9..
list.add(matrix);
}
}
return this;
}
public void printResults(){ //output results
for(ImageMatrix matrix: list){
System.out.println(matrix);
}
}
public Iterator<ImageMatrix> iterator() {
return this.list.iterator();
}
/// kNN implementation ///
public static int distance(int[] a, int[] b) {
int sum = 0;
for(int i = 0; i < a.length; i++) {
sum += (a[i] - b[i]) * (a[i] - b[i]);
}
return (int)Math.sqrt(sum);
}
public static int classify(ImageMatrixDB trainingSet, int[] curData) {
int label = 0, bestDistance = Integer.MAX_VALUE;
for(ImageMatrix matrix: trainingSet) {
int dist = distance(matrix.getData(), curData);
if(dist < bestDistance) {
bestDistance = dist;
label = matrix.getClassCode();
}
}
return label;
}
public int size() {
return list.size(); //returns size of the list
}
public static void main(String[] argv) throws IOException {
ImageMatrixDB trainingSet = new ImageMatrixDB();
ImageMatrixDB validationSet = new ImageMatrixDB();
trainingSet.load("cw2DataSet1.csv");
validationSet.load("cw2DataSet2.csv");
int numCorrect = 0;
for(ImageMatrix matrix:validationSet) {
if(classify(trainingSet, matrix.getData()) == matrix.getClassCode()) numCorrect++;
} //285 correct
System.out.println("Accuracy: " + (double)numCorrect / validationSet.size() * 100 + "%");
System.out.println();
}

In the for loop of classify you are trying to find the training example that is closest to a test point. You need to switch that with a code that finds K of the training points that is the closest to the test data. Then you should call getClassCode for each of those K points and find the majority(i.e. the most frequent) of the class codes among them. classify will then return the major class code you found.
You may break the ties (i.e. having 2+ most frequent class codes assigned to equal number of training data) in any way that suits your need.
I am really inexperienced in Java, but just by looking around the language reference, I came up with the implementation below.
public static int classify(ImageMatrixDB trainingSet, int[] curData, int k) {
int label = 0, bestDistance = Integer.MAX_VALUE;
int[][] distances = new int[trainingSet.size()][2];
int i=0;
// Place distances in an array to be sorted
for(ImageMatrix matrix: trainingSet) {
distances[i][0] = distance(matrix.getData(), curData);
distances[i][1] = matrix.getClassCode();
i++;
}
Arrays.sort(distances, (int[] lhs, int[] rhs) -> lhs[0]-rhs[0]);
// Find frequencies of each class code
i = 0;
Map<Integer,Integer> majorityMap;
majorityMap = new HashMap<Integer,Integer>();
while(i < k) {
if( majorityMap.containsKey( distances[i][1] ) ) {
int currentValue = majorityMap.get(distances[i][1]);
majorityMap.put(distances[i][1], currentValue + 1);
}
else {
majorityMap.put(distances[i][1], 1);
}
++i;
}
// Find the class code with the highest frequency
int maxVal = -1;
for (Entry<Integer, Integer> entry: majorityMap.entrySet()) {
int entryVal = entry.getValue();
if(entryVal > maxVal) {
maxVal = entryVal;
label = entry.getKey();
}
}
return label;
}
All you need to do is adding K as a parameter. Keep in mind, however, that the code above does not handle ties in a particular way.

JAVA error cannot find a symbol

I need to create a JAVA method: public static int[] Numb() that reads and returns a series of positive integer values. If the user enters -1 we should stop accepting values, and then I want to call it in the main method. And we should return to the user integers that he entered them, with the total number.
So if he entered the following:
5 6 1 2 3 -1
So the total number is : 6
The numbers entered are: 5 6 1 2 3 -1
I tried the following:
class Ideone
{
public static void main (String[] args) throws java.lang.Exception
{
// your code goes here
}
public static int[] readNumbers(int[] n)
{
int[] a = new int[n.length];
Scanner scan = new Scanner(System.in);
for(int i = 0;i<n.length;i++) {
String token = scan.next();
a[i] = Integer.nextString();
}
}
}
And here is a fiddle of them. I have an error that said:
Main.java:21: error: cannot find symbol
a[i] = Integer.nextString();
I am solving this exercise step by step, and I am creating the method that reads integers. Any help is appreciated.

Integer.nextString() doesn't exist, to get the next entered integer value, you may change your loop to either :
for(int i = 0;i<n.length;i++) {
a[i] = scan.nextInt();
}
or as #vikingsteve suggested :
for(int i = 0;i<n.length;i++) {
String token = scan.next();
a[i] = Integer.parseInt(token);
}

public static void main(String[] args) {
List<Integer> numList = new ArrayList<>();
initializeList(numList);
System.out.println("Num of integer in list: "+numList.size());
}
public static void initializeList(List<Integer> numList) {
Scanner sc = new Scanner(System.in);
boolean flag = true;
while(flag) {
int num = sc.nextInt();
if(num==-1) {
flag = false;
}else {
numList.add(num);
}
}
sc.close();
}
Since the number of integers is unknown, use ArrayList. It's size can be altered unlike arrays.
You can create something like arraylist on your own..it can be done like this:
public class Test {
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
CustomArray c = new CustomArray(3);
boolean flag = true;
while (flag) {
int num = sc.nextInt();
if (num == -1) {
flag = false;
} else {
c.insert(num);
}
System.out.println(Arrays.toString(c.numList));
}
sc.close();
}
}
class CustomArray {
int[] numList;
int size; // size of numList[]
int numOfElements; // integers present in numList[]
public CustomArray(int size) {
// TODO Auto-generated constructor stub
numList = new int[size];
this.size = size;
numOfElements = 0;
}
void insert(int num) {
if (numOfElements < size) {
numList[numOfElements++] = num;
} else {
// list is full
size = size * 2; //double the size, you can use some other factor as well
//create a new list with new size
int[] newList = new int[size];
for (int i = 0; i < numOfElements; i++) {
//copy all the elements in new list
newList[i] = numList[i];
}
numList = newList;//make numList equal to new list
numList[numOfElements++] = num;
}
}
}

Quick Sort in java in not running if the first element is the largest while considering first element as pivot

I have written a code in java for quicksort while considering the first element as pivot. The code is giving an ArrayOutOfBoundsException if I consider the first element as the largest element of the array. While the logic is running perfectly when implemented the same logic in C++.
import java.util.Scanner;
class QSort
{
private int n;
private int a[] = new int[n];
public QSort(int[] x)
{
n = x.length;
a = x;
}
private int qs(int low,int up)
{
int pivot = a[low];
int p = low+1,q = up;
while(q>=p)
{
while(pivot>=a[p])
p++;
while(pivot<a[q])
q--;
if(q>p)
{
a[p]=a[p]+a[q]-(a[q]=a[p]); //swapping(a[p],a[q])
p++;
q--;
}
}
a[low]=a[low]+a[q]-(a[q]=a[low]); //swapping(a[low],a[q])
return q;
}
public void quicksort(int low,int up)
{
if(low<up)
{
int i = qs(low,up);
quicksort(low,i-1);
quicksort(i+1,up);
}
}
public void print()
{
System.out.println("\nThe sorted array is :");
for(int i=0; i<a.length; i++)
{
System.out.println(a[i]);
}
}
}
class Quick
{
public static void main(String args[])
{
System.out.print("\nEnter the no. of values : ");
Scanner sc = new Scanner(System.in);
int n = sc.nextInt();
int x[] = new int[n];
System.out.println("\nEnter the elements :");
for(int i=0; i<n; i++)
x[i] = sc.nextInt();
QSort s = new QSort(x);
s.quicksort(0,n-1);
s.print();
}
}

How to get array method from another array method from the other class

My apologize, I have a class on my Project, called test01.java. And i used the library from Tadaki Graphlib contained many class. On of them is Graph.java.
Test01.java:
public class test01 extends Graph{
public test01(String name, int n) {
super(name);
public test01(String name, int n) {
super(name);
graphLib.Vertex vList[] = new graphLib.Vertex[n];
for (int i = 0; i < n; i++) {
vList[i] = new graphLib.Vertex(String.valueOf(i));
addVertex(vList[i]);
}
int deg = 0;
System.out.println("<---------- Random val ---------->");
addArc(vList[0], vList[1], String.valueOf(0)); deg++;
addArc(vList[1], vList[0], String.valueOf(1)); deg++;
System.out.println("Vertex-0 with Vertex-1");
System.out.println("Vertex-1 with Vertex-0");
int k = 2;
int l;
int m=0;
Random randomval = new Random();
int isAvailInt [] = new int[n];
while (k<n) {
for(l=0;l<k;l++){
isAvailInt [l]= Integer.parseInt(vList[l].toString());
m=isAvailInt[l];
}
int chosen = randomval.nextInt(m);
addArc(vList[k], vList[chosen], String.valueOf(k));
System.out.println("Vertex-"+k+" with Vertex-"+chosen+
" exp = " + String.valueOf(k));
k++;
}
}public static void main(String args[]) {
int n;
String num = JOptionPane.showInputDialog("Masukkan nilai jumlah iterasi = ");
String degnum = null;
n = Integer.parseInt(num);
int deg []= new int [n];
test01 t = new test01("test",n);
System.out.println("<---------- Vertex-i = Degree-i ------------>");
graphLib.Graph g= new Graph("test");
int [][]adj = g.getAdjacent();
System.out.println(adj[0][0]);
for (int i=0; i<t.getSize();i++){
for (int j=0; j<t.getSize();j++){
}
}}
and one other class called Graph.java
public class Graph extends GraphBase { int adjacent[][] = null;
public Graph(String name) {
this.name = name;
vertexes = Utils.createVertexList();
arcs = Utils.createArcList();
a2vHead = new HashMap<>();
a2vTail = new HashMap<>();
v2a = new HashMap<>();
}
public int[][] getAdjacent() {
int n = vertexes.size();
adjacent = new int[n][];
for (int i = 0; i < n; i++) {
adjacent[i] = new int[n];
for (int j = 0; j < n; j++) {
adjacent[i][j] = 0;
}
}
if (directed) {
for (int i = 0; i < n; i++) {
Vertex v = vertexes.get(i);
for (Arc a : v2a.get(v)) {
Vertex t = a2vTail.get(a);
int l = vertexes.indexOf(t);
adjacent[l][i]++;
}
}
} else {
for (int i = 0; i < n; i++) {
Vertex v = vertexes.get(i);
for (Arc a : v2a.get(v)) {
Vertex t = a2vTail.get(a);
if (!t.equals(v)) {
int l = vertexes.indexOf(t);
adjacent[i][l]++;
adjacent[l][i]++;
}
}
}
}
checkConnectedness();
return adjacent;
}}
From above, method - int [][] Adjacent() - has an array return value:
return adjacent;
Then I want to received it with array variable declared:
int [][]adj = g.getAdjacent();
But when I run the program, the code :
System.out.println(adj[0][0]);
Has appeared error :
Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 0
I've declare the variable vertexes in Graph.java that extended from other class, GraphBase.java:
vertexes = Utils.createVertexList();
How do I obtain an array value form a variable adjacent in Graph.java to test01.java and how do I display it with System.out.println() ?

Well you haven't shown where vertexes is initialized (or even declared) in Graph. I suspect it's empty, so when you execute this code:
public int[][] getAdjacent() {
int n = vertexes.size();
adjacent = new int[n][];
...
return adjacent;
}
... you'll end up with an empty array. That would cause the problem you've seen. You can easily check the size in your main method:
System.out.println(adj.length);
I suspect you'll find it's 0. Either that, or adj[0].length is 0.
It's not clear how you expect the Graph to find any vertexes - you don't supply it with any, or even the value of n. You just call the constructor with a string:
graphLib.Graph g= new Graph("test");
Unless that's meant to be the name of a file which is loaded in the constructor, there's nowhere for it to get data from. You need to take a step back and think about where you expect the data to come from, then make sure that it can actually flow through your program. The problem isn't getting the array reference back to main - the problem is that the array is empty.

I doubted about this line returning 0.
int n = vertexes.size();
You can reproduce this issue by running below code
int adjacent[][] = new int[0][];
System.out.println(adjacent[0][0]);
You will get the same exception
Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 0
To solve this issue
Make sure before proceeding vertexes have expected values.