countBy() function

返回每个组中对象数量的计数。类似于 groupBy,但不返回值列表,而是返回该组中值数量的计数。

Signature:

declare function countBy<A, B extends Key>(
  f: (a: A) => B,
  iterable: Iterable<A>,
): {
  [K in B]: number;
};

Example

const given = [
  { category: "clothes", desc: "good" },
  { category: "pants", desc: "bad" },
  { category: "shoes", desc: "not bad" },
  { category: "shoes", desc: "great" },
  { category: "pants", desc: "good" },
];

countBy((a) => a.category, given);
//{
//  clothes: 1,
//  pants: 2,
//  shoes: 2,
// };

Try It

Open Source Code