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keyBy
Convert a collection to an object whose keys are determined by a provided function and whose values are the collection values.
Installation
npm install @stdlib/utils-key-by
Usage
var keyBy = require( '@stdlib/utils-key-by' );
keyBy( collection, fcn[, thisArg ] )
Converts a collection
to an object whose keys are determined by a provided function
and whose values are the collection
values.
function toKey( value ) {
return value.a;
}
var arr = [
{ 'a': 1 },
{ 'a': 2 }
];
var out = keyBy( arr, toKey );
// returns { '1': { 'a': 1 }, '2': { 'a': 2 } }
The invoked function
is provided two arguments:
-
value
: collection element -
index
: collection index
To set the function execution context, provide a thisArg
.
function toKey( value, index ) {
this.sum += value;
this.count += 1;
return index;
}
var arr = [ 1, 2, 3, 4 ];
var context = {
'sum': 0,
'count': 0
};
var out = keyBy( arr, toKey, context );
// returns { '0': 1, '1': 2, '2': 3, '3': 4 }
var mean = context.sum / context.count;
// returns 2.5
Notes
- A
collection
may be either anArray
,Typed Array
, or an array-likeObject
(excludingstrings
andfunctions
). - If more than one element in a
collection
resolves to the same key, the key value is thecollection
element which last resolved to the key. - Object values are shallow copies.
Examples
var keyBy = require( '@stdlib/utils-key-by' );
var arr;
var obj;
var i;
function toKey( value ) {
return value.name;
}
arr = new Array( 100 );
for ( i = 0; i < arr.length; i++ ) {
arr[ i ] = {
'name': 'v'+i,
'value': i
};
}
obj = keyBy( arr, toKey );
console.log( obj );
See Also
-
@stdlib/utils-for-each
: invoke a function for each element in a collection.
Notice
This package is part of stdlib, a standard library for JavaScript and Node.js, with an emphasis on numerical and scientific computing. The library provides a collection of robust, high performance libraries for mathematics, statistics, streams, utilities, and more.
For more information on the project, filing bug reports and feature requests, and guidance on how to develop stdlib, see the main project repository.
Community
License
See LICENSE.
Copyright
Copyright © 2016-2024. The Stdlib Authors.