feat: add stats/incr/nanmse

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

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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.
+
+-->
+
+# incrnanmse
+
+> Compute the [mean squared error][mean-squared-error] (MSE) incrementally, ignoring `NaN` values.
+
+<section class="intro">
+
+The [mean squared error][mean-squared-error] is defined as
+
+<!-- <equation class="equation" label="eq:mean_squared_error" align="center" raw="\operatorname{MSE} = \frac{1}{n} \sum_{i=0}^{n-1} (y_i - x_i)^2" alt="Equation for the mean squared error."> -->
+
+```math
+\mathop{\mathrm{MSE}} = \frac{1}{n} \sum_{i=0}^{n-1} (y_i - x_i)^2
+```
+
+<!-- <div class="equation" align="center" data-raw-text="\operatorname{MSE} = \frac{1}{n} \sum_{i=0}^{n-1} (y_i - x_i)^2" data-equation="eq:mean_squared_error">
+    <img src="https://cdn.jsdelivr.net/gh/stdlib-js/stdlib@f5d4f0cac0a117ba1e0c70706a2fb284f69e7291/lib/node_modules/@stdlib/stats/incr/nanmse/docs/img/equation_mean_squared_error.svg" alt="Equation for the mean squared error.">
+    <br>
+</div> -->
+
+<!-- </equation> -->
+
+</section>
+
+<!-- /.intro -->
+
+<section class="usage">
+
+## Usage
+
+```javascript
+var incrnanmse = require( '@stdlib/stats/incr/nanmse' );
+```
+
+#### incrnanmse()
+
+Returns an accumulator `function` which incrementally computes the [mean squared error][mean-squared-error], ignoring `NaN` values.
+
+```javascript
+var accumulator = incrnanmse();
+```
+
+#### accumulator( \[x, y] )
+
+If provided input values `x` and `y`, the accumulator function returns an updated [mean squared error][mean-squared-error]. If not provided input values `x` and `y`, the accumulator function returns the current [mean squared error][mean-squared-error].
+
+```javascript
+var accumulator = incrnanmse();
+
+var m = accumulator( 2.0, 3.0 );
+// returns 1.0
+
+m = accumulator( 1.0, NaN );
+// returns 1.0
+
+m = accumulator( -1.0, -4.0 );
+// returns 5.0
+
+m = accumulator( -3.0, 5.0 );
+// returns ~24.67
+
+m = accumulator();
+// returns ~24.67
+```
+
+</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.
+
+</section>
+
+<!-- /.notes -->
+
+<section class="examples">
+
+## Examples
+
+<!-- eslint no-undef: "error" -->
+
+```javascript
+var bernoulli = require( '@stdlib/random/base/bernoulli' );
+var uniform = require( '@stdlib/random/base/uniform' );
+var incrnanmse = require( '@stdlib/stats/incr/nanmse' );
+
+var accumulator;
+var v1;
+var v2;
+var i;
+
+// Initialize an accumulator:
+accumulator = incrnanmse();
+
+// For each simulated datum, update the mean squared error...
+for ( i = 0; i < 100; i++ ) {
+    v1 = ( bernoulli( 0.8 ) < 1 ) ? NaN : uniform( -50.0, 50.0 );
+    v2 = ( bernoulli( 0.8 ) < 1 ) ? NaN : uniform( -50.0, 50.0 );
+    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">
+
+</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-squared-error]: https://en.wikipedia.org/wiki/Mean_squared_error
+
+</section>
+
+<!-- /.links -->

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

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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 randu = require( '@stdlib/random/base/randu' );
+var pkg = require( './../package.json' ).name;
+var incrnanmse = require( './../lib' );
+
+
+// MAIN //
+
+bench( pkg, function benchmark( b ) {
+	var f;
+	var i;
+	b.tic();
+	for ( i = 0; i < b.iterations; i++ ) {
+		f = incrnanmse();
+		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( pkg+'::accumulator', function benchmark( b ) {
+	var acc;
+	var v;
+	var i;
+
+	acc = incrnanmse();
+
+	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();
+});

lib/node_modules/@stdlib/stats/incr/nanmse/docs/repl.txt

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+
+{{alias}}()
+    Returns an accumulator function which incrementally computes the mean
+    squared error (MSE), ignoring `NaN` values.
+
+    If provided input values, the accumulator function returns an updated mean
+    squared error. If not provided input values, the accumulator function
+    returns the current mean squared error.
+
+    Returns
+    -------
+    acc: Function
+        Accumulator function.
+
+    Examples
+    --------
+    > var accumulator = {{alias}}();
+    > var m = accumulator()
+    null
+    > m = accumulator( 2.0, 3.0 )
+    1.0
+    > m = accumulator( 1.0, NaN )
+    1.0
+    > m = accumulator( -5.0, 2.0 )
+    25.0
+    > m = accumulator()
+    25.0
+
+    See Also
+    --------

lib/node_modules/@stdlib/stats/incr/nanmse/docs/types/index.d.ts

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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.
+*/
+
+// TypeScript Version: 4.1
+
+/// <reference types="@stdlib/types"/>
+
+/**
+* If provided input values, the accumulator function returns an updated mean squared error. If not provided input values, the accumulator function returns the current mean squared error.
+*
+* @param x - input value
+* @param y - input value
+* @returns mean squared error or null
+*/
+type accumulator = ( x?: number, y?: number ) => number | null;
+
+/**
+* Returns an accumulator function which incrementally computes the mean squared error, ignoring `NaN` values.
+*
+* @returns accumulator function
+*
+* @example
+* var accumulator = incrnanmse();
+*
+* var m = accumulator();
+* // returns null
+*
+* m = accumulator( 2.0, 3.0 );
+* // returns 1.0
+*
+*
+* m = accumulator( 1.0, NaN );
+* // returns 1.0
+*
+* m = accumulator( -5.0, 2.0 );
+* // returns 25.0
+*
+* m = accumulator();
+* // returns 25.0
+*/
+declare function incrnanmse(): accumulator;
+
+
+// EXPORTS //
+
+export = incrnanmse;