How to count duplicate value in an array in javasc

Question

Currently, I got an array like that:

var uniqueCount = Array();

After a few steps, my array looks like that:

uniqueCount = [a,b,c,d,d,e,a,b,c,f,g,h,h,h,e,a];

How can I count how many a,b,c are there in the array? I want to have a result like:

a = 3
b = 1
c = 2
d = 2

etc.

Answer 1

Something like this:

    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);

Use a simple for loop instead of forEach if you don't want this to break in older browsers.

Answer 2

I think this is the simplest way how to count occurrences with same value in array.

var a = [true, false, false, false];
a.filter(function(value){
    return value === false;
}).length                                      

Answer 3

You can solve it without using any for/while loops ou forEach.

function myCounter(inputWords) {        
    return inputWords.reduce( (countWords, word) => {
        countWords[word] = ++countWords[word] || 1;
        return countWords;
    }, {});
}

Hope it helps you!

Answer 4

var uniqueCount = ['a','b','c','d','d','e','a','b','c','f','g','h','h','h','e','a'];
// here we will collect only unique items from the array
var uniqueChars = [];

// iterate through each item of uniqueCount
for (i of uniqueCount) {
// if this is an item that was not earlier in uniqueCount, 
// put it into the uniqueChars array
  if (uniqueChars.indexOf(i) == -1) {
    uniqueChars.push(i);
  } 
}
// after iterating through all uniqueCount take each item in uniqueChars
// and compare it with each item in uniqueCount. If this uniqueChars item 
// corresponds to an item in uniqueCount, increase letterAccumulator by one.
for (x of uniqueChars) {
  let letterAccumulator = 0;
  for (i of uniqueCount) {
    if (i == x) {letterAccumulator++;}
  }
  console.log(`${x} = ${letterAccumulator}`);
}

Answer 5

A combination of good answers:

var count = {};
var arr = ['a', 'b', 'c', 'd', 'd', 'e', 'a', 'b', 'c', 'f', 'g', 'h', 'h', 'h', 'e', 'a'];
var iterator = function (element) {
    count[element] = (count[element] || 0) + 1;
}

if (arr.forEach) {
    arr.forEach(function (element) {
        iterator(element);
    });
} else {
    for (var i = 0; i < arr.length; i++) {
        iterator(arr[i]);
    }
}  

Hope it's helpful.

Answer 6

By using array.map we can reduce the loop, see this on jsfiddle

function Check(){
    var arr = Array.prototype.slice.call(arguments);
    var result = [];
    for(i=0; i< arr.length; i++){
        var duplicate = 0;
        var val = arr[i];
        arr.map(function(x){
            if(val === x) duplicate++;
        })
        result.push(duplicate>= 2);
    }
    return result;
}

To Test:

var test = new Check(1,2,1,4,1);
console.log(test);