javascript - Idiomatically find the number of occurrences a given value has in an array

Question

I have an array with repeating values. I would like to find the number of occurrences for any given value.

For example, if I have an array defined as so: var dataset = [2,2,4,2,6,4,7,8];, I want to find the number of occurrences of a certain value in the array. That is, the program should show that if I have 3 occurrences of the value 2, 1 occurrence of the value 6, and so on.

What's the most idiomatic/elegant way to do this?

Answer 1

reduce is more appropriate here than filter as it doesn't build a temporary array just for counting.

var dataset = [2,2,4,2,6,4,7,8];
var search = 2;

var count = dataset.reduce(function(n, val) {
    return n + (val === search);
}, 0);

console.log(count);