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feat: add blas/ext/last-index-of
PR-URL: #7665 Ref: #2656 Co-authored-by: Athan Reines <[email protected]> Reviewed-by: Athan Reines <[email protected]> Co-authored-by: stdlib-bot <[email protected]>
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‎lib/node_modules/@stdlib/blas/ext/last-index-of/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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# lastIndexOf
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> Return the last index of a specified search element along an [ndarray][@stdlib/ndarray/ctor] dimension.
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<section class="usage">
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## Usage
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```javascript
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var lastIndexOf = require( '@stdlib/blas/ext/last-index-of' );
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```
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#### lastIndexOf( x, searchElement\[, fromIndex]\[, options] )
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Returns the last index of a specified search element along an [ndarray][@stdlib/ndarray/ctor] dimension.
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```javascript
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var array = require( '@stdlib/ndarray/array' );
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// Create an input ndarray:
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var x = array( [ 1.0, 2.0, 3.0, 2.0, 5.0, 6.0 ] );
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// returns <ndarray>
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// Perform operation:
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var out = lastIndexOf( x, 2.0 );
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// returns <ndarray>
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var idx = out.get();
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// returns 3
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```
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The function has the following parameters:
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- **x**: input [ndarray][@stdlib/ndarray/ctor]. Must have at least one dimension.
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- **searchElement**: search element. May be either a scalar value or an [ndarray][@stdlib/ndarray/ctor]. If provided a scalar value, the value is cast to the data type of the input [ndarray][@stdlib/ndarray/ctor]. If provided an [ndarray][@stdlib/ndarray/ctor], the value must have a shape which is [broadcast-compatible][@stdlib/ndarray/base/broadcast-shapes] with the non-reduced dimensions of the input [ndarray][@stdlib/ndarray/ctor]. For example, given the input shape `[2, 3, 4]` and `options.dim=0`, the search element [ndarray][@stdlib/ndarray/ctor] must have a shape which is [broadcast-compatible][@stdlib/ndarray/base/broadcast-shapes] with the shape `[3, 4]`.
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- **fromIndex**: index from which to begin searching (_optional_). May be either a scalar value or an [ndarray][@stdlib/ndarray/ctor] having an integer index or "generic" [data type][@stdlib/ndarray/dtypes]. If provided an [ndarray][@stdlib/ndarray/ctor], the value must have a shape which is [broadcast-compatible][@stdlib/ndarray/base/broadcast-shapes] with the non-reduced dimensions of the input [ndarray][@stdlib/ndarray/ctor]. For example, given the input shape `[2, 3, 4]` and `options.dim=0`, a provided [ndarray][@stdlib/ndarray/ctor] must have a shape which is [broadcast-compatible][@stdlib/ndarray/base/broadcast-shapes] with the shape `[3, 4]`. If provided a negative integer, the index at which to begin searching along a dimension is determined by counting backward from the last element (where `-1` refers to the last element). Default: `-1`.
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- **options**: function options (_optional_).
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The function accepts the following options:
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- **dtype**: output ndarray [data type][@stdlib/ndarray/dtypes]. Must be an integer index or generic [data type][@stdlib/ndarray/dtypes].
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- **dim**: dimension over which to perform operation. If provided a negative integer, the dimension along which to perform the operation is determined by counting backward from the last dimension (where `-1` refers to the last dimension). Default: `-1`.
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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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If the function is unable to find a search element along an [ndarray][@stdlib/ndarray/ctor], the corresponding element in the returned [ndarray][@stdlib/ndarray/ctor] is `-1`.
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```javascript
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var array = require( '@stdlib/ndarray/array' );
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// Create an input ndarray:
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var x = array( [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0 ] );
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// returns <ndarray>
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// Perform operation:
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var out = lastIndexOf( x, 10.0 );
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// returns <ndarray>
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var idx = out.get();
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// returns -1
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```
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By default, the function begins searching from the last element along the reduction dimension. To begin searching from a different index, provide a `fromIndex` argument.
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```javascript
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var array = require( '@stdlib/ndarray/array' );
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// Create an input ndarray:
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var x = array( [ 1.0, 2.0, 3.0, 4.0, 2.0, 6.0 ] );
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// returns <ndarray>
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// Perform operation:
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var out = lastIndexOf( x, 2.0, 3 );
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// returns <ndarray>
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var idx = out.get();
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// returns 1
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```
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By default, the function performs the operation over elements in the last dimension. To perform the operation over a different dimension, provide a `dim` 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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var x = array( [ [ -3.0, 2.0 ], [ -3.0, 4.0 ] ] );
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var out = lastIndexOf( x, -3.0, {
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'dim': 0
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});
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// returns <ndarray>
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var idx = ndarray2array( out );
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// returns [ 1, -1 ]
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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 array = require( '@stdlib/ndarray/array' );
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var ndarray2array = require( '@stdlib/ndarray/to-array' );
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var x = array( [ [ -3.0, 2.0 ], [ -3.0, 4.0 ] ] );
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var opts = {
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'dim': 0,
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'keepdims': true
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};
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var out = lastIndexOf( x, -3.0, opts );
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// returns <ndarray>
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var idx = ndarray2array( out );
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// returns [ [ 1, -1 ] ]
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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 ndarray2array = require( '@stdlib/ndarray/to-array' );
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var dtype = require( '@stdlib/ndarray/dtype' );
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var array = require( '@stdlib/ndarray/array' );
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var x = array( [ 1.0, 2.0, 3.0, 4.0 ] );
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var idx = lastIndexOf( x, 2.0, {
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'dtype': 'generic'
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});
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// returns <ndarray>
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var dt = dtype( idx );
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// returns 'generic'
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```
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#### lastIndexOf.assign( x, searchElement\[, fromIndex], out\[, options] )
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Returns the last index of a specified search element along an [ndarray][@stdlib/ndarray/ctor] dimension 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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var x = array( [ 1.0, 2.0, 3.0, 2.0, 5.0, 6.0 ] );
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var y = zeros( [], {
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'dtype': 'int32'
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});
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var out = lastIndexOf.assign( x, 2.0, y );
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// returns <ndarray>
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var idx = out.get();
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// returns 3
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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]. Must have at least one dimension.
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- **searchElement**: search element. May be either a scalar value or an [ndarray][@stdlib/ndarray/ctor]. If provided a scalar value, the value is cast to the data type of the input [ndarray][@stdlib/ndarray/ctor]. If provided an [ndarray][@stdlib/ndarray/ctor], the value must have a shape which is [broadcast-compatible][@stdlib/ndarray/base/broadcast-shapes] with the non-reduced dimensions of the input [ndarray][@stdlib/ndarray/ctor]. For example, given the input shape `[2, 3, 4]` and `options.dim=0`, the search element [ndarray][@stdlib/ndarray/ctor] must have a shape which is [broadcast-compatible][@stdlib/ndarray/base/broadcast-shapes] with the shape `[3, 4]`.
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- **fromIndex**: index from which to begin searching (_optional_). May be either a scalar value or an [ndarray][@stdlib/ndarray/ctor] having an integer index or "generic" [data type][@stdlib/ndarray/dtypes]. If provided an [ndarray][@stdlib/ndarray/ctor], the value must have a shape which is [broadcast-compatible][@stdlib/ndarray/base/broadcast-shapes] with the non-reduced dimensions of the input [ndarray][@stdlib/ndarray/ctor]. For example, given the input shape `[2, 3, 4]` and `options.dim=0`, a provided [ndarray][@stdlib/ndarray/ctor] must have a shape which is [broadcast-compatible][@stdlib/ndarray/base/broadcast-shapes] with the shape `[3, 4]`. If provided a negative integer, the index at which to begin searching along a dimension is determined by counting backward from the last element (where `-1` refers to the last element). Default: `-1`.
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- **out**: output [ndarray][@stdlib/ndarray/ctor].
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- **options**: function options (_optional_).
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The method accepts the following options:
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- **dim**: dimension over which to perform operation. If provided a negative integer, the dimension along which to perform the operation is determined by counting backward from the last dimension (where `-1` refers to the last dimension). Default: `-1`.
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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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- 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 an integer index 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 discreteUniform = require( '@stdlib/random/array/discrete-uniform' );
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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 lastIndexOf = require( '@stdlib/blas/ext/last-index-of' );
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// Generate an array of random numbers:
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var xbuf = discreteUniform( 10, 0, 20, {
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'dtype': 'float64'
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});
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// Wrap in an ndarray:
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var x = new ndarray( 'float64', xbuf, [ 5, 2 ], [ 2, 1 ], 0, 'row-major' );
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console.log( ndarray2array( x ) );
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// Perform operation:
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var idx = lastIndexOf( x, 10.0, {
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'dim': 0
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});
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// Print the results:
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console.log( ndarray2array( idx ) );
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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 -->

‎lib/node_modules/@stdlib/blas/ext/last-index-of/benchmark/benchmark.assign.js‎

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/**
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* @license Apache-2.0
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*
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* Copyright (c) 2025 The Stdlib Authors.
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*
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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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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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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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'use strict';
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// MODULES //
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var bench = require( '@stdlib/bench' );
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var isnan = require( '@stdlib/math/base/assert/is-nan' );
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var pow = require( '@stdlib/math/base/special/pow' );
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var uniform = require( '@stdlib/random/array/uniform' );
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var zeros = require( '@stdlib/ndarray/zeros' );
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var ndarray = require( '@stdlib/ndarray/base/ctor' );
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var pkg = require( './../package.json' ).name;
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var lastIndexOf = require( './../lib' );
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// VARIABLES //
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var options = {
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'dtype': 'float64'
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};
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// FUNCTIONS //
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/**
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* Creates a benchmark function.
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*
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* @private
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* @param {PositiveInteger} len - array length
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* @returns {Function} benchmark function
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*/
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function createBenchmark( len ) {
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var out;
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var x;
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x = uniform( len, -50.0, 50.0, options );
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x = new ndarray( options.dtype, x, [ len ], [ 1 ], 0, 'row-major' );
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out = zeros( [], {
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'dtype': 'int32'
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});
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return benchmark;
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/**
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* Benchmark function.
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*
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* @private
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* @param {Benchmark} b - benchmark instance
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*/
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function benchmark( b ) {
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var o;
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var i;
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b.tic();
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for ( i = 0; i < b.iterations; i++ ) {
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o = lastIndexOf.assign( x, 100.0, out );
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if ( typeof o !== 'object' ) {
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b.fail( 'should return an ndarray' );
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}
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}
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b.toc();
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if ( isnan( o.get() ) ) {
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b.fail( 'should not return NaN' );
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}
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b.pass( 'benchmark finished' );
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b.end();
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}
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}
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// MAIN //
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/**
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* Main execution sequence.
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*
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* @private
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*/
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function main() {
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var len;
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var min;
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var max;
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var f;
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var i;
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min = 1; // 10^min
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max = 6; // 10^max
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for ( i = min; i <= max; i++ ) {
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len = pow( 10, i );
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f = createBenchmark( len );
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bench( pkg+':assign:dtype='+options.dtype+',len='+len, f );
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}
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}
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main();

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