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feat: add ndarray/find-last
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‎lib/node_modules/@stdlib/ndarray/find-last/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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# findLast
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> Return a new [ndarray][@stdlib/ndarray/ctor] containing the first elements which pass a test implemented by a predicate function along one or more [ndarray][@stdlib/ndarray/ctor] dimensions.
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<section class="intro">
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</section>
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<!-- /.intro -->
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<section class="usage">
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## Usage
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```javascript
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var findLast = require( '@stdlib/ndarray/find-last' );
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```
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#### findLast( x\[, options], predicate\[, thisArg] )
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Returns a new [ndarray][@stdlib/ndarray/ctor] containing the last elements which pass a test implemented by a predicate function along one or more [ndarray][@stdlib/ndarray/ctor] dimensions.
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<!-- eslint-disable no-invalid-this, max-len -->
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```javascript
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var array = require( '@stdlib/ndarray/array' );
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function isEven( value ) {
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return value % 2.0 === 0.0;
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}
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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 ], [ 7.0, 8.0 ] ] ] );
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// returns <ndarray>
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// Perform reduction:
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var out = findLast( x, isEven );
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// returns <ndarray>
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var v = out.get();
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// returns 8.0
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```
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The function accepts the following arguments:
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- **x**: input [ndarray][@stdlib/ndarray/ctor].
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- **options**: function options _(optional)_.
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- **predicate**: predicate function.
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- **thisArg**: predicate function execution context _(optional)_.
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The function accepts the following options:
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- **dims**: list of dimensions over which to perform a reduction.
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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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- **sentinelValue**: value to return when no element passes the test. May be either a scalar value or a zero-dimensional [ndarray][@stdlib/ndarray/ctor].
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By default, the function performs reduction over all all elements in a provided [ndarray][@stdlib/ndarray/ctor]. To reduce specific dimensions, set the `dims` option.
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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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function isEven( value ) {
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return value % 2.0 === 0.0;
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}
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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 ], [ 7.0, 8.0 ] ] ] );
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// returns <ndarray>
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var opts = {
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'dims': [ 0 ]
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};
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// Perform reduction:
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var out = findLast( x, opts, isEven );
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// returns <ndarray>
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var v = ndarray2array( out );
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// returns [ [ 8.0, NaN ], [ 6.0, NaN ] ]
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```
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By default, the function returns an [ndarray][@stdlib/ndarray/ctor] having a shape matching only the non-reduced dimensions of the input [ndarray][@stdlib/ndarray/ctor] (i.e., the reduced dimensions are dropped). To include the reduced dimensions as singleton dimensions in the output [ndarray][@stdlib/ndarray/ctor], 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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function isEven( value ) {
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return value % 2.0 === 0.0;
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}
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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 ], [ 7.0, 8.0 ] ] ] );
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// returns <ndarray>
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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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// Perform reduction:
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var out = findLast( x, opts, isEven );
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// returns <ndarray>
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var v = ndarray2array( out );
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// returns [ [ [ 8.0, NaN ], [ 6.0, NaN ] ] ]
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```
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To specify a custom sentinel value to return when no element passes the test, set the `sentinelValue` option.
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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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function isEven( value ) {
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return value % 2.0 === 0.0;
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}
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// Create an input ndarray:
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var x = array( [ [ [ 1.0, 3.0 ], [ 5.0, 7.0 ] ], [ [ 9.0, 11.0 ], [ 13.0, 15.0 ] ] ] );
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// returns <ndarray>
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var opts = {
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'sentinelValue': -999
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};
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// Perform reduction:
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var out = findLast( x, opts, isEven );
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// returns <ndarray>
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var v = out.get();
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// returns -999
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```
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To set the `predicate` function 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 ndarray2array = require( '@stdlib/ndarray/to-array' );
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function isEven( value ) {
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this.count += 1;
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return value % 2.0 === 0.0;
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}
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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 ], [ 7.0, 8.0 ] ] ] );
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// returns <ndarray>
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var ctx = {
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'count': 0
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};
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// Perform reduction:
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var out = findLast( x, isEven, ctx );
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// returns <ndarray>
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var v = out.get();
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// returns 8.0
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var count = ctx.count;
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// returns 1
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```
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#### findLast.assign( x, out\[, options], predicate\[, thisArg] )
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Finds the last elements which pass a test implemented by a predicate function along one or more [ndarray][@stdlib/ndarray/ctor] dimensions 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 empty = require( '@stdlib/ndarray/empty' );
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function isEven( value ) {
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return value % 2.0 === 0.0;
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}
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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 ], [ 7.0, 8.0 ] ] ] );
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// returns <ndarray>
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// Create an output ndarray:
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var y = empty( [], {
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'dtype': x.dtype
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});
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// Perform reduction:
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var out = findLast.assign( x, y, isEven );
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// returns <ndarray>
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var bool = ( out === y );
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// returns true
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var v = y.get();
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// returns 8.0
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```
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The function accepts the following arguments:
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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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- **predicate**: predicate function.
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- **thisArg**: predicate function execution context _(optional)_.
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The function accepts the following options:
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- **dims**: list of dimensions over which to perform a reduction.
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- **sentinelValue**: value to return when no element passes the test. May be either a scalar value or a zero-dimensional [ndarray][@stdlib/ndarray/ctor].
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```javascript
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var array = require( '@stdlib/ndarray/array' );
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var empty = require( '@stdlib/ndarray/empty' );
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var ndarray2array = require( '@stdlib/ndarray/to-array' );
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function isEven( value ) {
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return value % 2.0 === 0.0;
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}
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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 ], [ 7.0, 8.0 ] ] ] );
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// returns <ndarray>
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// Create an output ndarray:
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var y = empty( [ 2, 2 ], {
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'dtype': x.dtype
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});
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var opts = {
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'dims': [ 0 ]
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};
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// Perform reduction:
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var out = findLast.assign( x, y, opts, isEven );
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var bool = ( out === y );
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// returns true
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var v = ndarray2array( y );
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// returns [ [ 8.0, NaN ], [ 6.0, NaN ] ]
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```
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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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- By default, when no `sentinelValue` is provided, the function returns a default sentinel value based on the input [ndarray][@stdlib/ndarray/ctor] [data-type][@stdlib/ndarray/dtypes]:
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- real-valued floating-point data types: `NaN`.
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- complex-valued floating-point data types: `NaN + NaNj`.
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- integer data types: maximum value.
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- boolean data types: `false`.
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- The `predicate` function is provided the following arguments:
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- **value**: current array element.
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- **indices**: current array element indices.
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- **arr**: the input [ndarray][@stdlib/ndarray/ctor].
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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 uniform = require( '@stdlib/random/uniform' );
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var isPositive = require( '@stdlib/assert/is-positive-number' ).isPrimitive;
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var ndarray2array = require( '@stdlib/ndarray/to-array' );
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var findLast = require( '@stdlib/ndarray/find-last' );
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var x = uniform( [ 2, 4, 5 ], -10.0, 10.0, {
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'dtype': 'float64'
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});
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console.log( ndarray2array( x ) );
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var y = findLast( x, isPositive );
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console.log( y.get() );
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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 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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<!-- <related-links> -->
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<!-- </related-links> -->
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</section>
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<!-- /.links -->

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