countAs - nodef/extra-lists GitHub Wiki

Count occurrences of values.

Alternatives: count, countAs.

function countAs(x, fm)
// x:  lists
// fm: map function (v, k, x)

const xlists = require('extra-lists');

var x = ['a', 'b', 'c', 'd', 'e'], [1, 1, 2, 2, 4](/nodef/extra-lists/wiki/'a',-'b',-'c',-'d',-'e'],-[1,-1,-2,-2,-4);
xlists.countAs(x);
// → Map(3) { 1 => 2, 2 => 2, 4 => 1 }

var x = ['a', 'b', 'c', 'd'], [1, 2, 3, 4](/nodef/extra-lists/wiki/'a',-'b',-'c',-'d'],-[1,-2,-3,-4);
xlists.countAs(x, v => v % 2);
// → Map(2) { 1 => 2, 0 => 2 }

References