JAVASCRIPT

how to find duplicates in an array

const numbers = [1, 2, 3, 2, 4, 5, 5, 6];

const set = new Set(numbers);

const duplicates = numbers.filter(item => {
    if (set.has(item)) {
        set.delete(item);
    } else {
        return item;
    }
});

console.log(duplicates);
// [ 2, 5 ]

find duplicates in array

function findDuplicates(arr) {
	const duplicates = new Set()
  
  return arr.filter(item => {
  	if (duplicates.has(item)) {
    	return true
    }
    duplicates.add(item)
    return false
  })
}

find duplicate element on array

const order = ["apple", "banana", "orange", "banana", "apple", "banana"];

const result = order.reduce(function (prevVal, item) {
    if (!prevVal[item]) {
        // if an object doesn't have a key yet, it means it wasn't repeated before
        prevVal[item] = 1;
    } else {
        // increase the number of repetitions by 1
        prevVal[item] += 1;
    }

    // and return the changed object
    return prevVal;
}, {}); // The initial value is an empty object.

console.log(result); // { apple: 2, banana: 3, orange: 1 } 

Find / Display duplicate numbers in array

var input = [1, 2, 5, 5, 3, 1, 3, 1];
    var duplicates = input.reduce(function(acc, el, i, arr) {
    if (arr.indexOf(el) !== i && acc.indexOf(el) < 0) acc.push(el); return acc;
    }, []);
    console.log(duplicates);

find-array-duplicates

npm i find-array-duplicates

import duplicates from 'find-array-duplicates'

const names = [
 { 'age': 36, 'name': 'Bob' },
 { 'age': 40, 'name': 'Harry' },
 { 'age': 1,  'name': 'Bob' }
]
 
duplicates(names, 'name').single()
// => { 'age': 36, 'name': 'Bob' }

find array is duplicate or not

  const numbers = [1, 2, 3, 2, 4, 5, 5, 6];

let isDuplicate = false;

// Outer for loop
for (let i = 0; i < numbers.length; i++) {
    // Inner for loop
    for (let j = 0; j < numbers.length; j++) {
        // Skip self comparison
        if (i !== j) {
            // Check for duplicate
            if (numbers[i] === numbers[j]) {
                isDuplicate = true;
                // Terminate inner loop
                break;
            }
        }
        // Terminate outer loop
        if (isDuplicate) {
            break;
        }
    }
}

if (!isDuplicate) {
    console.log(`Array doesn't contain duplicates.`);
} else {
    console.log(`Array contains duplicates.`);
}
// Output: Array contains duplicates.

duplicate array values

public class Main {
public static void main(String[] args) {
  int[] arr1 = {1,2,3,3,4};
  for (int i = 0; i < arr1.length-1 ; i++) {
    for (int j = 0; j < arr1.length; j++) {
      if (arr1[i]==arr1[j] && (j != i)){
      System.out.println("array's duplicate number: " +
      arr1[j]);
      	}
      }
    }
	}
}

array iteration + find duplicates

function lonelyinteger(a: number[]): number {
   for (let item of a) {
        const items = a.filter(el => item === el)
        if (items.length === 1) {
            return item
        }
    }
}



const a:number[] = [1,2,3,4,3,2,1]

const result:number = lonelyinteger(a);
console.log(result)