feat: add stats/incr/nanmmape

PR-URL: #9296
Closes: #5583

Co-authored-by: Philipp Burckhardt <pburckhardt@outlook.com>
Reviewed-by: Philipp Burckhardt <pburckhardt@outlook.com>
Signed-off-by: Nirmal Jyoti Biswas <59522492+nirmaljb@users.noreply.github.com>
Signed-off-by: Philipp Burckhardt <pburckhardt@outlook.com>

Author: nirmaljb

lib/node_modules/@stdlib/stats/incr/nanmmape/README.md

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+<!--
+
+@license Apache-2.0
+
+Copyright (c) 2026 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.
+
+-->
+
+# incrnanmmape
+
+> Compute a moving [mean absolute percentage error][mean-absolute-percentage-error] incrementally, ignoring `NaN` values.
+
+<section class="intro">
+
+For a window of size `W`, the [mean absolute percentage error][mean-absolute-percentage-error] is defined as
+
+<!-- <equation class="equation" label="eq:mean_absolute_percentage_error" align="center" raw="\operatorname{MAPE}  = \frac{100}{W} \sum_{i=0}^{W-1} \biggl| \frac{a_i - f_i}{a_i} \biggr|" alt="Equation for the mean absolute percentage error."> -->
+
+```math
+\mathop{\mathrm{MAPE}}  = \frac{100}{W} \sum_{i=0}^{W-1} \biggl| \frac{a_i - f_i}{a_i} \biggr|
+```
+
+<!-- <div class="equation" align="center" data-raw-text="\operatorname{MAPE}  = \frac{100}{W} \sum_{i=0}^{W-1} \biggl| \frac{a_i - f_i}{a_i} \biggr|" data-equation="eq:mean_absolute_percentage_error">
+    <img src="https://cdn.jsdelivr.net/gh/stdlib-js/stdlib@f13330c8d3bb837438b30381f6cd70dbccd4837c/lib/node_modules/@stdlib/stats/incr/mmape/docs/img/equation_mean_absolute_percentage_error.svg" alt="Equation for the mean absolute percentage error.">
+    <br>
+</div> -->
+
+<!-- </equation> -->
+
+where `f_i` is the forecast value and `a_i` is the actual value.
+
+</section>
+
+<!-- /.intro -->
+
+<section class="usage">
+
+## Usage
+
+```javascript
+var incrnanmmape = require( '@stdlib/stats/incr/nanmmape' );
+```
+
+#### incrnanmmape( window )
+
+Returns an accumulator `function` which incrementally computes a moving [mean absolute percentage error][mean-absolute-percentage-error]. The `window` parameter defines the number of values over which to compute the moving [mean absolute percentage error][mean-absolute-percentage-error], ignoring `NaN` values.
+
+```javascript
+var accumulator = incrnanmmape( 3 );
+```
+
+#### accumulator( \[f, a] )
+
+If provided input values `f` and `a`, the accumulator function returns an updated [mean absolute percentage error][mean-absolute-percentage-error]. If not provided input values `f` and `a`, the accumulator function returns the current [mean absolute percentage error][mean-absolute-percentage-error].
+
+```javascript
+var accumulator = incrnanmmape( 3 );
+
+var m = accumulator();
+// returns null
+
+// Fill the window...
+m = accumulator( 2.0, 3.0 ); // [(2.0,3.0)]
+// returns ~33.33
+
+m = accumulator( NaN, 3.0 ); // [(2.0,3.0)]
+// returns ~33.33
+
+m = accumulator( 1.0, 4.0 ); // [(2.0,3.0), (1.0,4.0)]
+// returns ~54.17
+
+m = accumulator( 3.0, 9.0 ); // [(2.0,3.0), (1.0,4.0), (3.0,9.0)]
+// returns ~58.33
+
+// Window begins sliding...
+m = accumulator( 7.0, 3.0 ); // [(1.0,4.0), (3.0,9.0), (7.0,3.0)]
+// returns ~91.67
+
+m = accumulator( 7.0, NaN ); // [(1.0,4.0), (3.0,9.0), (7.0,3.0)]
+// returns ~91.67
+
+m = accumulator( 5.0, 3.0 ); // [(3.0,9.0), (7.0,3.0), (5.0,3.0)]
+// returns ~88.89
+
+m = accumulator();
+// returns ~88.89
+```
+
+</section>
+
+<!-- /.usage -->
+
+<section class="notes">
+
+## Notes
+
+-   Input values are **not** type checked. If non-numeric inputs are possible, you are advised to type check and handle accordingly **before** passing the value to the accumulator function.
+
+-   As `W` (f,a) pairs are needed to fill the window buffer, the first `W-1` returned values are calculated from smaller sample sizes. Until the window is full, each returned value is calculated from all provided values.
+
+-   **Warning**: the [mean absolute percentage error][mean-absolute-percentage-error]  has several shortcomings:
+
+    -   The measure is **not** suitable for intermittent demand patterns (i.e., when `a_i` is `0`).
+    -   The [mean absolute percentage error][mean-absolute-percentage-error] is not symmetrical, as the measure cannot exceed 100% for forecasts which are too "low" and has no limit for forecasts which are too "high".
+    -   When used to compare the accuracy of forecast models (e.g., predicting demand), the measure is biased toward forecasts which are too low.
+
+</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 incrnanmmape = require( '@stdlib/stats/incr/nanmmape' );
+
+var accumulator;
+var v1;
+var v2;
+var i;
+
+// Initialize an accumulator:
+accumulator = incrnanmmape( 5 );
+
+// For each simulated datum, update the moving mean absolute percentage error...
+for ( i = 0; i < 100; i++ ) {
+    v1 = ( bernoulli( 0.8 ) < 1 ) ? NaN : uniform( 0.0, 100.0 );
+    v2 = ( bernoulli( 0.8 ) < 1 ) ? NaN : uniform( 0.0, 100.0 );
+    accumulator( v1, v2 );
+}
+console.log( accumulator() );
+```
+
+</section>
+
+<!-- /.examples -->
+
+<!-- Section for related `stdlib` packages. Do not manually edit this section, as it is automatically populated. -->
+
+<section class="related">
+
+* * *
+
+## See Also
+
+-   <span class="package-name">[`@stdlib/stats/incr/mape`][@stdlib/stats/incr/mape]</span><span class="delimiter">: </span><span class="description">compute the mean absolute percentage error (MAPE) incrementally.</span>
+-   <span class="package-name">[`@stdlib/stats/incr/mmaape`][@stdlib/stats/incr/mmaape]</span><span class="delimiter">: </span><span class="description">compute a moving arctangent mean absolute percentage error (MAAPE) incrementally.</span>
+-   <span class="package-name">[`@stdlib/stats/incr/mmpe`][@stdlib/stats/incr/mmpe]</span><span class="delimiter">: </span><span class="description">compute a moving mean percentage error (MPE) incrementally.</span>
+-   <span class="package-name">[`@stdlib/stats/incr/mmean`][@stdlib/stats/incr/mmean]</span><span class="delimiter">: </span><span class="description">compute a moving arithmetic mean incrementally.</span>
+
+</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">
+
+[mean-absolute-percentage-error]: https://en.wikipedia.org/wiki/Mean_absolute_percentage_error
+
+<!-- <related-links> -->
+
+[@stdlib/stats/incr/mape]: https://github.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/stats/incr/mape
+
+[@stdlib/stats/incr/mmaape]: https://github.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/stats/incr/mmaape
+
+[@stdlib/stats/incr/mmpe]: https://github.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/stats/incr/mmpe
+
+[@stdlib/stats/incr/mmean]: https://github.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/stats/incr/mmean
+
+<!-- </related-links> -->
+
+</section>
+
+<!-- /.links -->

lib/node_modules/@stdlib/stats/incr/nanmmape/benchmark/benchmark.js

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+/**
+* @license Apache-2.0
+*
+* Copyright (c) 2026 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 randu = require( '@stdlib/random/base/randu' );
+var format = require( '@stdlib/string/format' );
+var pkg = require( './../package.json' ).name;
+var incrnanmmape = require( './../lib' );
+
+
+// MAIN //
+
+bench( pkg, function benchmark( b ) {
+	var f;
+	var i;
+	b.tic();
+	for ( i = 0; i < b.iterations; i++ ) {
+		f = incrnanmmape( (i%5)+1 );
+		if ( typeof f !== 'function' ) {
+			b.fail( 'should return a function' );
+		}
+	}
+	b.toc();
+	if ( typeof f !== 'function' ) {
+		b.fail( 'should return a function' );
+	}
+	b.pass( 'benchmark finished' );
+	b.end();
+});
+
+bench( format( '%s::accumulator', pkg ), function benchmark( b ) {
+	var acc;
+	var v;
+	var i;
+
+	acc = incrnanmmape( 5 );
+
+	b.tic();
+	for ( i = 0; i < b.iterations; i++ ) {
+		v = acc( randu()+0.5, randu()+0.5 );
+		if ( v !== v ) {
+			b.fail( 'should not return NaN' );
+		}
+	}
+	b.toc();
+	if ( v !== v ) {
+		b.fail( 'should not return NaN' );
+	}
+	b.pass( 'benchmark finished' );
+	b.end();
+});