CODEWITHSUNDEEP
javaarraysloops
Kabindra Shrestha
Kabindra Shrestha

Reputation: 333

Compare two array and return an array to show which elements are equal or not

I have two array. I want to compare two array and return an array which is the first array with elements equal or not equal to the other array. For example:

int[] arr1 = {1,2,3,4,5}; 
int[] arr2 = {1,3};

I want to return an array or hashmap that shows which elements are equal or not.

boolean[] arr = {true, false, true, false, false};

OR

HashMap<Integer, String> map = new HashMap<Integer, String>();           
map.put(1, "true");  
map.put(2, "false");  
map.put(3, "true");  
map.put(4, "false");  
map.put(5, "false");

Output: {1=true, 2=false, 3=true, 4=false, 5=false}

This is my code. This only shows equal values.

for (Int arr1 : arr1) {
        for (Int arr2 : arr2) {
            if (arr2.equals(arr1)) {
                booleanValue = true;
                System.err.println(arr2 + ", " + arr1 + ", " + booleanValue);
            }
        }
    }

Please help me out with the logic. Thank You

Upvotes: 2

Views: 2600

Answers (4)

fps
fps

Reputation: 34480

There's a nice way to do this with streams:

int[] arr1 = {1, 2, 3, 4, 5};
int[] arr2 = {1, 3};

Set<Integer> set2 = new HashSet<>();
for (int a : arr2) {
    set2.add(a);
}

Map<Integer, Boolean> map = Arrays.stream(arr1).boxed()
    .collect(Collectors.toMap(Function.identity(), set2::contains));

System.out.println(map); // {1=true, 2=false, 3=true, 4=false, 5=false}

First we create a HashSet from arr2, then we stream the elements of arr1, we box them (so we can collect them in the next step), and we finally collect the Integer elements of the stream into a map: the key is the actual Integer element, and the value is a boolean indicating whether this element belongs to set2 or not.

EDIT: If you want the values of the map to be strings instead of booleans, you can just change the value mapper function a little bit:

Map<Integer, String> map2 = Arrays.stream(arr1).boxed()
    .collect(Collectors.toMap(e -> e, e -> String.valueOf(set2.contains(e))));

System.out.println(map2); // {1=true, 2=false, 3=true, 4=false, 5=false}

Upvotes: 0

JUAN CALVOPINA M
JUAN CALVOPINA M

Reputation: 3984

In the second loop when comparing both matrices if they are equal you must set the flag to true and break the second loop, so the first loop will compare the next element, for example:

int[] arr1 = {1, 2, 3, 4, 5};
int[] arr2 = {1, 3};

HashMap<Integer, Boolean> map = new HashMap<>();

for (int i : arr1) {
    for (int j : arr2) {
        if (j == i) {
            map.put(i, true);
            break;
        } else {
            map.put(i, false);
        }
    }
}

System.out.println(Arrays.asList(map));

Output:

[{1=true, 2=false, 3=true, 4=false, 5=false}]

Upvotes: 0

Mohammed Bakr Sikal
Mohammed Bakr Sikal

Reputation: 357

I would do something like

public static void main(String[] args) {
    HashMap<Integer, Boolean> map = new HashMap<Integer, Boolean>();
    int[] arr1 = {1, 2, 3, 4, 5};
    int[] arr2 = {1, 3};
    for (int a : arr1) {
        map.put(a, isElementInArray(a, arr2));
    }

    System.out.println(Arrays.asList(map));
}

public static boolean isElementInArray(int element, int[] array) {
    for (int a : array) {
        if (a == element) {
            return true;
        }
    }
    return false;
}

Output: 

[{1=true, 2=false, 3=true, 4=false, 5=false}]

Upvotes: 0

Ashraful Islam
Ashraful Islam

Reputation: 12870

Instead of using foreach loop use fori loop. For each element of arr1 check for each element of arr2 if match then set the arr of that index true and break the loop. 

int[] arr1 = {1, 2, 3, 4, 5};
int[] arr2 = {1, 3};
boolean[] arr = new boolean[arr1.length];

for (int i = 0; i < arr1.length; i++) {
    for (int j = 0; j < arr2.length; j++) {
        if (arr1[i] == arr2[j]) {
            arr[i] = true;
        }
    }
}

System.out.println(Arrays.toString(arr));

Upvotes: 1

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