countBy
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2023-12-01
Creates a new ObjectLikeSequence containing the unique keys of all the elements in this sequence, each paired with the number of elements in this sequence having that key.
Signature
Sequence.countBy = function(keyFn) { /*...*/ }
Sequence.countBy = function countBy(keyFn) { return new CountedSequence(this, keyFn); }
Name | Type(s) | Description |
---|---|---|
keyFn | Function|string | The function to call on the elements in this sequence to obtain a key by which to count them, or a string representing a parameter to read from all the elements in this sequence. |
returns | Sequence | The new sequence. |
Examples
function oddOrEven(x) { return x % 2 === 0 ? 'even' : 'odd'; } var numbers = [1, 2, 3, 4, 5]; Lazy(numbers).countBy(oddOrEven) // sequence: { odd: 3, even: 2 } Lazy(numbers).countBy(oddOrEven).get("odd") // => 3 Lazy(numbers).countBy(oddOrEven).get("foo") // => undefined