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averageBy

TS JS Deno

Returns the average of an array, after mapping each element to a value using the provided function.

Use Array.prototype.map() to map each element to the value returned by fn, Array.prototype.reduce() to add each value to an accumulator, initialized with a value of 0, divide by the length of the array.

typescript
type NumCollector<T> = (item: T) => number;
const averageBy = <T = any>(arr: T[], fn: NumCollector<T> | string) => {
  const mapper = typeof fn === "function" ? fn : (val: any) => val[fn];
  return arr.reduce((acc, val) => acc + mapper(val), 0) / arr.length;
};
typescript
averageBy([{ n: 4 }, { n: 2 }, { n: 8 }, { n: 6 }], (o) => o.n); // 5
averageBy([{ n: 4 }, { n: 2 }, { n: 8 }, { n: 6 }], "n"); // 5