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<!--

@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
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# nanmaxBy

> Compute the maximum value of a one-dimensional ndarray via a callback function, ignoring `NaN` values.

<section class="intro">

</section>

<!-- /.intro -->

<section class="usage">

## Usage

```javascript
var nanmaxBy = require( '@stdlib/stats/base/ndarray/nanmax-by' );
```

#### nanmaxBy( arrays, clbk\[, thisArg ] )

Computes the maximum value of a one-dimensional ndarray via a callback function, ignoring `NaN` values.

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

function clbk( value ) {
return value * 2.0;
}

var xbuf = [ 1.0, NaN, 4.0, 2.0 ];
var x = new ndarray( 'generic', xbuf, [ 4 ], [ 1 ], 0, 'row-major' );

var v = nanmaxBy( [ x ], clbk );
// returns 8.0
```

The function has the following parameters:

- **arrays**: array-like object containing a one-dimensional input ndarray.
- **clbk**: callback function.
- **thisArg**: callback execution context (_optional_).

The invoked callback is provided three arguments:

- **value**: current array element.
- **idx**: current array element index.
- **array**: input ndarray.

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

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

function clbk( value ) {
this.count += 1;
return value * 2.0;
}

var xbuf = [ 1.0, 3.0, NaN, 2.0 ];
var x = new ndarray( 'generic', xbuf, [ 4 ], [ 1 ], 0, 'row-major' );
var ctx = {
'count': 0
};

var v = nanmaxBy( [ x ], clbk, ctx );
// returns 6.0

var count = ctx.count;
// returns 4
```

</section>

<!-- /.usage -->

<section class="notes">

## Notes

- If provided an empty one-dimensional ndarray, the function returns `NaN`.
- A provided callback function should return a numeric value.
- If a provided callback function returns `NaN`, the value is ignored.
- If a provided callback function does not return any value (or equivalently, explicitly returns `undefined`), the value is **ignored**.

</section>

<!-- /.notes -->

<section class="examples">

## Examples

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

```javascript
var uniform = require( '@stdlib/random/base/uniform' );
var bernoulli = require( '@stdlib/random/base/bernoulli' );
var filledarrayBy = require( '@stdlib/array/filled-by' );
var ndarray = require( '@stdlib/ndarray/base/ctor' );
var ndarray2array = require( '@stdlib/ndarray/to-array' );
var nanmaxBy = require( '@stdlib/stats/base/ndarray/nanmax-by' );

function clbk( value ) {
return value * 2.0;
}

function rand() {
if ( bernoulli( 0.8 ) < 1 ) {
return NaN;
}
return uniform( -50.0, 50.0 );
}

var xbuf = filledarrayBy( 10, 'generic', rand );
var x = new ndarray( 'generic', xbuf, [ xbuf.length ], [ 1 ], 0, 'row-major' );
console.log( ndarray2array( x ) );

var v = nanmaxBy( [ x ], clbk );
console.log( v );
```

</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">

</section>

<!-- /.links -->
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/**
* @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 uniform = require( '@stdlib/random/base/uniform' );
var filledarrayBy = require( '@stdlib/array/filled-by' );
var bernoulli = require( '@stdlib/random/base/bernoulli' );
var isnan = require( '@stdlib/math/base/assert/is-nan' );
var pow = require( '@stdlib/math/base/special/pow' );
var ndarray = require( '@stdlib/ndarray/base/ctor' );
var pkg = require( './../package.json' ).name;
var nanmaxBy = require( './../lib' );


// VARIABLES //

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


// FUNCTIONS //

/**
* Accessor function.
*
* @private
* @param {number} value - array element
* @returns {number} accessed value
*/
function clbk( value ) {
return value * 2.0;
}

/**
* Returns a random number.
*
* @private
* @returns {number} random number
*/
function rand() {
if ( bernoulli( 0.8 ) < 1 ) {
return NaN;
}
return uniform( -10.0, 10.0 );
}

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

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

return benchmark;

function benchmark( b ) {
var v;
var i;

b.tic();
for ( i = 0; i < b.iterations; i++ ) {
v = nanmaxBy( [ x ], clbk );
if ( isnan( v ) ) {
b.fail( 'should not return NaN' );
}
}
b.toc();
if ( isnan( v ) ) {
b.fail( 'should not return NaN' );
}
b.pass( 'benchmark finished' );
b.end();
}
}


// MAIN //

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+':len='+len, f );
}
}

main();
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{{alias}}( arrays, clbk[, thisArg] )
Computes the maximum value of a one-dimensional ndarray via a callback
function, ignoring `NaN` values.

If provided an empty ndarray, the function returns `NaN`.

The callback function is provided three arguments:

- value: current array element.
- index: current array index.
- array: the input ndarray.

The callback function should return a numeric value.

If the callback function does not return any value (or equivalently,
explicitly returns `undefined`), the value is ignored.

If the callback function returns `NaN`, the value is ignored.

Parameters
----------
arrays: ArrayLikeObject<ndarray>
Array-like object containing a one-dimensional input ndarray.

clbk: Function
Callback function.

thisArg: any (optional)
Callback execution context.

Returns
-------
out: number
Maximum value.

Examples
--------
> var xbuf = [ 1.0, NaN, 2.0 ];
> var dt = 'generic';
> var sh = [ xbuf.length ];
> var sx = [ 1 ];
> var ox = 0;
> var ord = 'row-major';
> var x = new {{alias:@stdlib/ndarray/ctor}}( dt, xbuf, sh, sx, ox, ord );
> function f ( v ) { return v * 2.0; };
> {{alias}}( [ x ], f )
4.0

See Also
--------
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