Skip to content

feat: add blas/ext/last-index-of #7665

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Draft
wants to merge 1 commit into
base: develop
Choose a base branch
from
Draft

feat: add blas/ext/last-index-of #7665

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
260 changes: 260 additions & 0 deletions lib/node_modules/@stdlib/blas/ext/last-index-of/README.md
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -0,0 +1,260 @@
<!--

@license Apache-2.0

Copyright (c) 2025 The Stdlib Authors.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.

-->

# lastIndexOf

> Return the last index of a specified search element along an [ndarray][@stdlib/ndarray/ctor] dimension.

<section class="usage">

## Usage

```javascript
var lastIndexOf = require( '@stdlib/blas/ext/last-index-of' );
```

#### lastIndexOf( x, searchElement\[, fromIndex]\[, options] )

Returns the last index of a specified search element along an [ndarray][@stdlib/ndarray/ctor] dimension.

```javascript
var array = require( '@stdlib/ndarray/array' );

// Create an input ndarray:
var x = array( [ 1.0, 2.0, 3.0, 2.0, 5.0, 6.0 ] );
// returns <ndarray>

// Perform operation:
var out = lastIndexOf( x, 2.0 );
// returns <ndarray>

var idx = out.get();
// returns 3
```

The function has the following parameters:

- **x**: input [ndarray][@stdlib/ndarray/ctor]. Must have at least one dimension.
- **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]`.
- **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: `0`.
- **options**: function options (_optional_).

The function accepts the following options:

- **dtype**: output ndarray [data type][@stdlib/ndarray/dtypes]. Must be an integer index or generic [data type][@stdlib/ndarray/dtypes].
- **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`.
- **keepdims**: boolean indicating whether the reduced dimensions should be included in the returned [ndarray][@stdlib/ndarray/ctor] as singleton dimensions. Default: `false`.

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`.

```javascript
var array = require( '@stdlib/ndarray/array' );

// Create an input ndarray:
var x = array( [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0 ] );
// returns <ndarray>

// Perform operation:
var out = lastIndexOf( x, 10.0 );
// returns <ndarray>

var idx = out.get();
// returns -1
```

By default, the function begins searching from the first element along the reduction dimension. To begin searching from a different index, provide a `fromIndex` argument.

```javascript
var array = require( '@stdlib/ndarray/array' );

// Create an input ndarray:
var x = array( [ 1.0, 2.0, 3.0, 4.0, 2.0, 6.0 ] );
// returns <ndarray>

// Perform operation:
var out = lastIndexOf( x, 2.0, 3 );
// returns <ndarray>

var idx = out.get();
// returns 4
Comment on lines +92 to +96
Copy link
Member

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Suggested change
var out = lastIndexOf( x, 2.0, 3 );
// returns <ndarray>
var idx = out.get();
// returns 4
var out = lastIndexOf( x, 1.0, 3 );
// returns <ndarray>
var idx = out.get();
// returns -1

```

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.

```javascript
var ndarray2array = require( '@stdlib/ndarray/to-array' );
var array = require( '@stdlib/ndarray/array' );

var x = array( [ [ -3.0, 2.0 ], [ -3.0, 4.0 ] ] );

var out = lastIndexOf( x, -3.0, {
'dim': 0
});
// returns <ndarray>

var idx = ndarray2array( out );
// returns [ 1, -1 ]
```

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`.

```javascript
var array = require( '@stdlib/ndarray/array' );
var ndarray2array = require( '@stdlib/ndarray/to-array' );

var x = array( [ [ -3.0, 2.0 ], [ -3.0, 4.0 ] ] );

var opts = {
'dim': 0,
'keepdims': true
};

var out = lastIndexOf( x, -3.0, opts );
// returns <ndarray>

var idx = ndarray2array( out );
// returns [ [ 1, -1 ] ]
```

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.

```javascript
var ndarray2array = require( '@stdlib/ndarray/to-array' );
var dtype = require( '@stdlib/ndarray/dtype' );
var array = require( '@stdlib/ndarray/array' );

var x = array( [ 1.0, 2.0, 3.0, 4.0 ] );

var idx = lastIndexOf( x, 2.0, {
'dtype': 'generic'
});
// returns <ndarray>

var dt = dtype( idx );
// returns 'generic'
```

#### lastIndexOf.assign( x, searchElement\[, fromIndex], out\[, options] )

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].

```javascript
var array = require( '@stdlib/ndarray/array' );
var zeros = require( '@stdlib/ndarray/zeros' );

var x = array( [ 1.0, 2.0, 3.0, 2.0, 5.0, 6.0 ] );
var y = zeros( [], {
'dtype': 'int32'
});

var out = lastIndexOf.assign( x, 2.0, y );
// returns <ndarray>

var idx = out.get();
// returns 3

var bool = ( out === y );
// returns true
```

The method has the following parameters:

- **x**: input [ndarray][@stdlib/ndarray/ctor]. Must have at least one dimension.
- **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]`.
- **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: `0`.
- **out**: output [ndarray][@stdlib/ndarray/ctor].
- **options**: function options (_optional_).

The method accepts the following options:

- **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`.

</section>

<!-- /.usage -->

<section class="notes">

## Notes

- 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].
- 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].

</section>

<!-- /.notes -->

<section class="examples">

## Examples

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

```javascript
var discreteUniform = require( '@stdlib/random/array/discrete-uniform' );
var ndarray2array = require( '@stdlib/ndarray/to-array' );
var ndarray = require( '@stdlib/ndarray/ctor' );
var lastIndexOf = require( '@stdlib/blas/ext/last-index-of' );

// Generate an array of random numbers:
var xbuf = discreteUniform( 10, 0, 20, {
'dtype': 'float64'
});

// Wrap in an ndarray:
var x = new ndarray( 'float64', xbuf, [ 5, 2 ], [ 2, 1 ], 0, 'row-major' );
console.log( ndarray2array( x ) );

// Perform operation:
var idx = lastIndexOf( x, 10.0, {
'dim': 0
});

// Print the results:
console.log( ndarray2array( idx ) );
```

</section>

<!-- /.examples -->

<!-- Section for related `stdlib` packages. Do not manually edit this section, as it is automatically populated. -->

<section class="related">

</section>

<!-- /.related -->

<!-- Section for all links. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->

<section class="links">

[@stdlib/ndarray/ctor]: https://github.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/ndarray/ctor

[@stdlib/ndarray/dtypes]: https://github.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/ndarray/dtypes

[@stdlib/ndarray/output-dtype-policies]: https://github.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/ndarray/output-dtype-policies

[@stdlib/ndarray/base/broadcast-shapes]: https://github.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/ndarray/base/broadcast-shapes

</section>

<!-- /.links -->
113 changes: 113 additions & 0 deletions lib/node_modules/@stdlib/blas/ext/last-index-of/benchmark/benchmark.assign.js
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -0,0 +1,113 @@
/**
* @license Apache-2.0
*
* Copyright (c) 2025 The Stdlib Authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/

'use strict';

// MODULES //

var bench = require( '@stdlib/bench' );
var isnan = require( '@stdlib/math/base/assert/is-nan' );
var pow = require( '@stdlib/math/base/special/pow' );
var uniform = require( '@stdlib/random/array/uniform' );
var zeros = require( '@stdlib/ndarray/zeros' );
var ndarray = require( '@stdlib/ndarray/base/ctor' );
var pkg = require( './../package.json' ).name;
var lastIndexOf = require( './../lib' );


// VARIABLES //

var options = {
'dtype': 'float64'
};


// FUNCTIONS //

/**
* Creates a benchmark function.
*
* @private
* @param {PositiveInteger} len - array length
* @returns {Function} benchmark function
*/
function createBenchmark( len ) {
var out;
var x;

x = uniform( len, -50.0, 50.0, options );
x = new ndarray( options.dtype, x, [ len ], [ 1 ], 0, 'row-major' );

out = zeros( [], {
'dtype': 'int32'
});

return benchmark;

/**
* Benchmark function.
*
* @private
* @param {Benchmark} b - benchmark instance
*/
function benchmark( b ) {
var o;
var i;

b.tic();
for ( i = 0; i < b.iterations; i++ ) {
o = lastIndexOf.assign( x, 10.0, out );
if ( typeof o !== 'object' ) {
b.fail( 'should return an ndarray' );
}
}
b.toc();
if ( isnan( o.get() ) ) {
b.fail( 'should not return NaN' );
}
b.pass( 'benchmark finished' );
b.end();
}
}


// MAIN //

/**
* Main execution sequence.
*
* @private
*/
function main() {
var len;
var min;
var max;
var f;
var i;

min = 1; // 10^min
max = 6; // 10^max

for ( i = min; i <= max; i++ ) {
len = pow( 10, i );
f = createBenchmark( len );
bench( pkg+':assign:dtype='+options.dtype+',len='+len, f );
}
}

main();
Loading