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Value frequencies
JavaScript, Array, Object · Oct 19, 2020
Creates an object with the unique values of an array as keys and their frequencies as the values.
- Use
Array.prototype.reduce()to map unique values to an object's keys, adding to existing keys every time the same value is encountered.
const frequencies = arr =>
arr.reduce((a, v) => {
a[v] = a[v] ? a[v] + 1 : 1;
return a;
}, {});frequencies(['a', 'b', 'a', 'c', 'a', 'a', 'b']); // { a: 4, b: 2, c: 1 }
frequencies([...'ball']); // { b: 1, a: 1, l: 2 }More like this
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