count appearances in array javascript code example
Example 1: javascript Count the occurrences of a value in an array
const countOccurrences = (arr, val) => arr.reduce((a, v) => (v === val ? a + 1 : a), 0);
countOccurrences([2, 1, 3, 3, 2, 3], 2);
countOccurrences(['a', 'b', 'a', 'c', 'a', 'b'], 'a');
Example 2: Count frequency of array elements js
var arr = [5, 5, 5, 2, 2, 2, 2, 2, 9, 4]
const map = arr.reduce((acc, e) => acc.set(e, (acc.get(e) || 0) + 1), new Map());
console.info([...map.keys()])
console.info([...map.values()])
console.info([...map.entries()])