Creates an object with the unique values of an array as keys and their frequencies as the values.
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 }
JavaScript, Array
Creates an object from an array, using a function to map each value to a key.
JavaScript, Array
Creates an object from an array, using the specified key and excluding it from each value.
JavaScript, Array
Filters an array of objects based on a condition while also filtering out unspecified keys.