groupBy

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2023-12-01

Creates a new ObjectLikeSequence comprising the elements in this one, grouped together according to some key. The value associated with each key in the resulting object-like sequence is an array containing all of the elements in this sequence with that key.

Signature

Sequence.groupBy = function(keyFn, valFn) { /*...*/ }

Sequence.groupBy = function groupBy(keyFn, valFn) {
  return new GroupedSequence(this, keyFn, valFn);
}

Name	Type(s)	Description
keyFn	Function\|string	The function to call on the elements in this sequence to obtain a key by which to group them, or a string representing a parameter to read from all the elements in this sequence.
valFn	Function\|string	(Optional) The function to call on the elements in this sequence to assign to the value for each instance to appear in the group, or a string representing a parameter to read from all the elements in this sequence.
returns	ObjectLikeSequence	The new sequence.

Examples

function oddOrEven(x) {
  return x % 2 === 0 ? 'even' : 'odd';
}
function square(x) {
  return x*x;
}

var numbers = [1, 2, 3, 4, 5];

Lazy(numbers).groupBy(oddOrEven)                     // sequence: { odd: [1, 3, 5], even: [2, 4] }
Lazy(numbers).groupBy(oddOrEven).get("odd")          // => [1, 3, 5]
Lazy(numbers).groupBy(oddOrEven).get("foo")          // => undefined
Lazy(numbers).groupBy(oddOrEven, square).get("even") // => [4, 16]

Lazy([
  { name: 'toString' },
  { name: 'toString' }
]).groupBy('name');
// => sequence: {
  'toString': [
{ name: 'toString' },
{ name: 'toString' }
  ]
}