GitHub 6219★

Count the occurrences of array elements

JavaScript version

const countOccurrences = (arr) => arr.reduce((prev, curr) => ((prev[curr] = ++prev[curr] || 1), prev), {});

TypeScript version

const countOccurrences = <T extends string | number,>(arr: T[]): Record<T, number> => (
arr.reduce((prev, curr) => ((prev[curr] = ++prev[curr] || 1), prev), {}as Record<T, number>)
);

Examples

countOccurrences([2, 1, 3, 3, 2, 3]); // { '1': 1, '2': 2, '3': 3 }
countOccurrences(['a', 'b', 'a', 'c', 'a', 'b']); // { 'a': 3, 'b': 2, 'c': 1 }
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