time-to-botec/squiggle/node_modules/@stdlib/utils/key-by-right/README.md

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# keyByRight

> Convert a collection to an object whose keys are determined by a provided function and whose values are the collection values, iterating from right to left.

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<section class="usage">

## Usage

```javascript
var keyByRight = require( '@stdlib/utils/key-by-right' );
```

#### keyByRight( collection, fcn\[, thisArg ] )

Converts a `collection` to an object whose keys are determined by a provided `function` and whose values are the `collection` values, iterating from right to left.

<!-- eslint-disable object-curly-newline -->

```javascript
function toKey( value ) {
    return value.a;
}

var arr = [
    { 'a': 1 },
    { 'a': 2 }
];

var out = keyByRight( arr, toKey );
// returns { '2': { 'a': 2 }, '1': { 'a': 1 } }
```

The invoked `function` is provided two arguments:

-   `value`: collection element
-   `index`: collection index

To set the function execution context, provide a `thisArg`.

```javascript
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 = keyByRight( arr, toKey, context );
// returns { '3': 4, '2': 3, '1': 2, '0': 1 }

var mean = context.sum / context.count;
// returns 2.5
```

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## Notes

-   A `collection` may be either an [`Array`][mdn-array], [`Typed Array`][mdn-typed-array], or an array-like [`Object`][mdn-object] (excluding `strings` and `functions`).
-   If more than one element in a `collection` resolves to the same key, the key value is the `collection` element which last resolved to the key.
-   Object values are shallow copies.

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## Examples

<!-- eslint no-undef: "error" -->

```javascript
var keyByRight = require( '@stdlib/utils/key-by-right' );

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 = keyByRight( arr, toKey );
console.log( obj );
```

</section>

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[mdn-array]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array

[mdn-typed-array]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray

[mdn-object]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object

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