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feat: add stats/min-by
PR-URL: #7792 Co-authored-by: Athan Reines <[email protected]> Reviewed-by: Athan Reines <[email protected]>
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‎lib/node_modules/@stdlib/stats/min-by/README.md

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<!--
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@license Apache-2.0
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Copyright (c) 2025 The Stdlib Authors.
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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-->
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# minBy
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> Compute the minimum value along one or more [ndarray][@stdlib/ndarray/ctor] dimensions according to a callback function.
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<section class="usage">
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## Usage
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```javascript
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var minBy = require( '@stdlib/stats/min-by' );
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```
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#### minBy( x\[, options], clbk\[, thisArg] )
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Computes the minimum value along one or more [ndarray][@stdlib/ndarray/ctor] dimensions according to a callback function.
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```javascript
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var array = require( '@stdlib/ndarray/array' );
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var x = array( [ -1.0, 2.0, -3.0 ] );
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function clbk( v ) {
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return v * 2.0;
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}
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var y = minBy( x, clbk );
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// returns <ndarray>
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var v = y.get();
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// returns -6.0
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```
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The function has the following parameters:
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- **x**: input [ndarray][@stdlib/ndarray/ctor].
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- **options**: function options (_optional_).
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- **clbk**: callback function.
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- **thisArg**: callback function execution context (_optional_).
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The invoked callback is provided three arguments:
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- **value**: current array element.
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- **idx**: current array element index.
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- **array**: input ndarray.
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To set the callback execution context, provide a `thisArg`.
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<!-- eslint-disable no-invalid-this -->
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```javascript
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var array = require( '@stdlib/ndarray/array' );
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var x = array( [ -1.0, 2.0, -3.0 ] );
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function clbk( v ) {
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this.count += 1;
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return v * 2.0;
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}
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var ctx = {
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'count': 0
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};
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var y = minBy( x, clbk, ctx );
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// returns <ndarray>
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var v = y.get();
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// returns -6.0
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var count = ctx.count;
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// returns 3
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```
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The function accepts the following options:
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- **dims**: list of dimensions over which to perform a reduction. If not provided, the function performs a reduction over all elements in a provided input [ndarray][@stdlib/ndarray/ctor].
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- **dtype**: output ndarray [data type][@stdlib/ndarray/dtypes]. Must be a real-valued or "generic" [data type][@stdlib/ndarray/dtypes].
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- **keepdims**: boolean indicating whether the reduced dimensions should be included in the returned [ndarray][@stdlib/ndarray/ctor] as singleton dimensions. Default: `false`.
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By default, the function performs a reduction over all elements in a provided input [ndarray][@stdlib/ndarray/ctor]. To perform a reduction over specific dimensions, provide a `dims` option.
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```javascript
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var ndarray2array = require( '@stdlib/ndarray/to-array' );
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var array = require( '@stdlib/ndarray/array' );
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function clbk( v ) {
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return v * 100.0;
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}
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var x = array( [ -1.0, 2.0, -3.0, 4.0 ], {
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'shape': [ 2, 2 ],
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'order': 'row-major'
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});
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var v = ndarray2array( x );
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// returns [ [ -1.0, 2.0 ], [ -3.0, 4.0 ] ]
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var opts = {
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'dims': [ 0 ]
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};
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var y = minBy( x, opts, clbk );
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// returns <ndarray>
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v = ndarray2array( y );
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// returns [ -300.0, 200.0 ]
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opts = {
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'dims': [ 1 ]
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};
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y = minBy( x, opts, clbk );
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// returns <ndarray>
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v = ndarray2array( y );
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// returns [ -100.0, -300.0 ]
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opts = {
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'dims': [ 0, 1 ]
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};
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y = minBy( x, opts, clbk );
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// returns <ndarray>
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v = y.get();
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// returns -300.0
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```
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By default, the function excludes reduced dimensions from the output [ndarray][@stdlib/ndarray/ctor]. To include the reduced dimensions as singleton dimensions, set the `keepdims` option to `true`.
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```javascript
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var ndarray2array = require( '@stdlib/ndarray/to-array' );
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var array = require( '@stdlib/ndarray/array' );
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function clbk( v ) {
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return v * 100.0;
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}
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var x = array( [ -1.0, 2.0, -3.0, 4.0 ], {
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'shape': [ 2, 2 ],
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'order': 'row-major'
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});
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var v = ndarray2array( x );
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// returns [ [ -1.0, 2.0 ], [ -3.0, 4.0 ] ]
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var opts = {
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'dims': [ 0 ],
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'keepdims': true
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};
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var y = minBy( x, opts, clbk );
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// returns <ndarray>
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v = ndarray2array( y );
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// returns [ [ -300.0, 200.0 ] ]
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opts = {
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'dims': [ 1 ],
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'keepdims': true
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};
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y = minBy( x, opts, clbk );
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// returns <ndarray>
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v = ndarray2array( y );
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// returns [ [ -100.0 ], [ -300.0 ] ]
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opts = {
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'dims': [ 0, 1 ],
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'keepdims': true
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};
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y = minBy( x, opts, clbk );
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// returns <ndarray>
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v = ndarray2array( y );
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// returns [ [ -300.0 ] ]
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```
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By default, the function returns an [ndarray][@stdlib/ndarray/ctor] having a [data type][@stdlib/ndarray/dtypes] determined by the function's output data type [policy][@stdlib/ndarray/output-dtype-policies]. To override the default behavior, set the `dtype` option.
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```javascript
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var getDType = require( '@stdlib/ndarray/dtype' );
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var array = require( '@stdlib/ndarray/array' );
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function clbk( v ) {
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return v * 100.0;
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}
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var x = array( [ -1.0, 2.0, -3.0 ], {
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'dtype': 'generic'
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});
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var opts = {
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'dtype': 'float64'
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};
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var y = minBy( x, opts, clbk );
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// returns <ndarray>
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var dt = getDType( y );
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// returns 'float64'
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```
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#### minBy.assign( x, out\[, options], clbk\[, thisArg] )
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Computes the minimum value along one or more [ndarray][@stdlib/ndarray/ctor] dimensions according to a callback function and assigns results to a provided output [ndarray][@stdlib/ndarray/ctor].
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```javascript
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var array = require( '@stdlib/ndarray/array' );
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var zeros = require( '@stdlib/ndarray/zeros' );
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function clbk( v ) {
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return v * 100.0;
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}
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var x = array( [ -1.0, 2.0, -3.0 ] );
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var y = zeros( [] );
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var out = minBy.assign( x, y, clbk );
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// returns <ndarray>
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var v = out.get();
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// returns -300.0
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var bool = ( out === y );
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// returns true
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```
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The method has the following parameters:
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- **x**: input [ndarray][@stdlib/ndarray/ctor].
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- **out**: output [ndarray][@stdlib/ndarray/ctor].
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- **options**: function options (_optional_).
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- **clbk**: callback function.
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- **thisArg**: callback execution context (_optional_).
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The method accepts the following options:
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- **dims**: list of dimensions over which to perform a reduction. If not provided, the function performs a reduction over all elements in a provided input [ndarray][@stdlib/ndarray/ctor].
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</section>
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<!-- /.usage -->
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<section class="notes">
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## Notes
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- A provided callback function should return a numeric value.
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- If a provided callback function does not return any value (or equivalently, explicitly returns `undefined`), the value is **ignored**.
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- Setting the `keepdims` option to `true` can be useful when wanting to ensure that the output [ndarray][@stdlib/ndarray/ctor] is [broadcast-compatible][@stdlib/ndarray/base/broadcast-shapes] with ndarrays having the same shape as the input [ndarray][@stdlib/ndarray/ctor].
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- The output data type [policy][@stdlib/ndarray/output-dtype-policies] only applies to the main function and specifies that, by default, the function must return an [ndarray][@stdlib/ndarray/ctor] having a real-valued or "generic" [data type][@stdlib/ndarray/dtypes]. For the `assign` method, the output [ndarray][@stdlib/ndarray/ctor] is allowed to have any supported output [data type][@stdlib/ndarray/dtypes].
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</section>
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<!-- /.notes -->
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<section class="examples">
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## Examples
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<!-- eslint no-undef: "error" -->
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```javascript
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var filledarrayBy = require( '@stdlib/array/filled-by' );
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var discreteUniform = require( '@stdlib/random/base/discrete-uniform' );
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var getDType = require( '@stdlib/ndarray/dtype' );
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var ndarray2array = require( '@stdlib/ndarray/to-array' );
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var ndarray = require( '@stdlib/ndarray/ctor' );
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var minBy = require( '@stdlib/stats/min-by' );
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// Define a function for generating an object having a random value:
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function random() {
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return {
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'value': discreteUniform( 0, 20 )
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};
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}
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// Generate an array of random objects:
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var xbuf = filledarrayBy( 25, 'generic', random );
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// Wrap in an ndarray:
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var x = new ndarray( 'generic', xbuf, [ 5, 5 ], [ 5, 1 ], 0, 'row-major' );
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console.log( ndarray2array( x ) );
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// Define an accessor function:
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function accessor( v ) {
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return v.value * 100;
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}
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// Perform a reduction:
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var opts = {
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'dims': [ 0 ]
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};
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var y = minBy( x, opts, accessor );
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// Resolve the output array data type:
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var dt = getDType( y );
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console.log( dt );
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// Print the results:
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console.log( ndarray2array( y ) );
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```
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</section>
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<!-- /.examples -->
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<!-- Section for related `stdlib` packages. Do not manually edit this section, as it is automatically populated. -->
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<section class="related">
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</section>
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<!-- /.related -->
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<!-- Section for all links. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->
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<section class="links">
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[@stdlib/ndarray/ctor]: https://github.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/ndarray/ctor
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[@stdlib/ndarray/dtypes]: https://github.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/ndarray/dtypes
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[@stdlib/ndarray/output-dtype-policies]: https://github.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/ndarray/output-dtype-policies
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[@stdlib/ndarray/base/broadcast-shapes]: https://github.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/ndarray/base/broadcast-shapes
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</section>
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<!-- /.links -->

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