how to count duplicates in an array javascript code example

Example 1: count duplicates array js

uniqueCount = ["a","b","c","d","d","e","a","b","c","f","g","h","h","h","e","a"];
var count = {};
uniqueCount.forEach(function(i) { count[i] = (count[i]||0) + 1;});
console.log(count);

Example 2: javascript get duplicates in array

function getDuplicateArrayElements(arr){
    var sorted_arr = arr.slice().sort();
    var results = [];
    for (var i = 0; i < sorted_arr.length - 1; i++) {
        if (sorted_arr[i + 1] === sorted_arr[i]) {
            results.push(sorted_arr[i]);
        }
    }
    return results;
}

var colors = ["red","orange","blue","green","red","blue"];
var duplicateColors= getDuplicateArrayElements(colors);//["blue", "red"]

Example 3: counting duplicate values javascript

var counts = {};
your_array.forEach(function(x) { counts[x] = (counts[x] || 0)+1; });

Example 4: how to count duplicates in an array javascript

arr.reduce((b,c)=>((b[b.findIndex(d=>d.el===c)]||b[b.push({el:c,count:0})-1]).count++,b),[]);

Example 5: function that duplicates data in array js

function doubleValues(array) {
  var newArray = [];
  array.forEach(function (el) { newArray.push(el, el); });    
  return newArray;
}

console.log(doubleValues([1,2,3]));

Example 6: check for duplicates in array javascript

[1, 2, 2, 4, 3, 4].filter((e, i, a) => a.indexOf(e) !== i) // [2, 4]