Browse through an array for a specific amount of values

Question

I have an array like this:

var arr = [a,a,b,b,b,c]

The result(a new array) should only show all the values which are exactly 2 times in this array, e.g.: a

Do you guys know how I could realize this? Thanks

Answer 1

You can first create object and add properties with forEach loop and then use filter on Object.keys to return array as result.

var arr = ['a','a','b','b','b','c'];

var o = {}
arr.forEach(e => o[e] = (o[e] || 0) + 1);
var result = Object.keys(o).filter(e => o[e] == 2);

console.log(result)

Answer 2

Please try this code:

var arr = ['a','a','b','b','b','c'];

var numberOfOccurrences = {};

arr.forEach(function (item) {
    numberOfOccurrences[item] = (numberOfOccurrences[item] || 0) + 1;
});

var duplicates = Object.keys(numberOfOccurrences).filter(function (item) { return numberOfOccurrences[item] === 2 });

console.log(duplicates);