Counts occurrences of values.

Alternatives: one, one-map, all-map. This is part of package extra-array.

array.countAllOn(x, [fn], [ths]);
// x:   an array
// fn:  map function (v, i, x)
// ths: this argument
// --> occurrences

const array = require('extra-array');

var x = [1, 1, 2, 2, 4];
array.countOn(x, 2);
// 2           ^  ^

var x = [1, 1, 2, 2, 4];
array.countOn(x, 3, v => v % 2);
// 2     ^  ^

references

• count-array-values: @zeke
• _.countBy(): lodash
• List-Extra.count(): elm