130 lines
3.2 KiB
Markdown
130 lines
3.2 KiB
Markdown
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@license Apache-2.0
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Copyright (c) 2019 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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# incrwmean
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> Compute a [weighted arithmetic mean][weighted-arithmetic-mean] incrementally.
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<section class="intro">
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The [weighted arithmetic mean][weighted-arithmetic-mean] is defined as
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<!-- <equation class="equation" label="eq:weighted_arithmetic_mean" align="center" raw="\bar{x} = \frac{\sum_{i=0}^{n-1} w_{i} x_{i}}{\sum_{i=0}^{n-1} w_{i}}" alt="Equation for the weighted arithmetic mean."> -->
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<div class="equation" align="center" data-raw-text="\bar{x} = \frac{\sum_{i=0}^{n-1} w_{i} x_{i}}{\sum_{i=0}^{n-1} w_{i}}" data-equation="eq:weighted_arithmetic_mean">
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<img src="https://cdn.jsdelivr.net/gh/stdlib-js/stdlib@adbea9806383f70c982e3191475c874efba1296b/lib/node_modules/@stdlib/stats/incr/wmean/docs/img/equation_weighted_arithmetic_mean.svg" alt="Equation for the weighted arithmetic mean.">
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<br>
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</div>
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<!-- </equation> -->
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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 incrwmean = require( '@stdlib/stats/incr/wmean' );
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```
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#### incrwmean()
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Returns an accumulator `function` which incrementally computes a [weighted arithmetic mean][weighted-arithmetic-mean].
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```javascript
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var accumulator = incrwmean();
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```
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#### accumulator( \[x, w] )
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If provided an input value `x` and a weight `w`, the accumulator function returns an updated weighted mean. If not provided any input values, the accumulator function returns the current mean.
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```javascript
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var accumulator = incrwmean();
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var mu = accumulator( 2.0, 1.0 );
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// returns 2.0
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mu = accumulator( 2.0, 0.5 );
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// returns 2.0
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mu = accumulator( 3.0, 1.5 );
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// returns 2.5
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mu = accumulator();
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// returns 2.5
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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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- Input values are **not** type checked. If provided `NaN` or a value which, when used in computations, results in `NaN`, the accumulated value is `NaN` for **all** future invocations. If non-numeric inputs are possible, you are advised to type check and handle accordingly **before** passing the value to the accumulator function.
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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 randu = require( '@stdlib/random/base/randu' );
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var incrwmean = require( '@stdlib/stats/incr/wmean' );
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var accumulator;
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var v;
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var w;
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var i;
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// Initialize an accumulator:
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accumulator = incrwmean();
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// For each simulated datum, update the weighted mean...
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for ( i = 0; i < 100; i++ ) {
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v = randu() * 100.0;
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w = randu() * 100.0;
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accumulator( v, w );
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}
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console.log( accumulator() );
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```
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</section>
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<!-- /.examples -->
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<section class="links">
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[weighted-arithmetic-mean]: https://en.wikipedia.org/wiki/Weighted_arithmetic_mean
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</section>
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<!-- /.links -->
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