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‎lib/node_modules/@stdlib/stats/dmean/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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# dmean
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> Compute the [arithmetic mean][arithmetic-mean] of a double-precision floating-point [ndarray][@stdlib/ndarray/ctor] along one or more dimensions.
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<section class="intro">
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The [arithmetic mean][arithmetic-mean] is defined as
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<!-- <equation class="equation" label="eq:arithmetic_mean" align="center" raw="\mu = \frac{1}{n} \sum_{i=0}^{n-1} x_i" alt="Equation for the arithmetic mean."> -->
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```math
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\mu = \frac{1}{n} \sum_{i=0}^{n-1} x_i
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```
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<!-- <div class="equation" align="center" data-raw-text="\mu = \frac{1}{n} \sum_{i=0}^{n-1} x_i" data-equation="eq:arithmetic_mean">
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<img src="https://cdn.jsdelivr.net/gh/stdlib-js/stdlib@42d8f64d805113ab899c79c7c39d6c6bac7fe25c/lib/node_modules/@stdlib/stats/strided/dmean/docs/img/equation_arithmetic_mean.svg" alt="Equation for the 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 dmean = require( '@stdlib/stats/dmean' );
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```
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#### dmean( x\[, options] )
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Computes the [arithmetic mean][arithmetic-mean] of a double-precision floating-point [ndarray][@stdlib/ndarray/ctor] along one or more dimensions.
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```javascript
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var array = require( '@stdlib/ndarray/array' );
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var x = array( [ 1.0, 2.0, -2.0, 4.0 ] );
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var y = dmean( x );
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// returns <ndarray>
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var v = y.get();
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// returns 1.25
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```
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The function has the following parameters:
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- **x**: input [ndarray][@stdlib/ndarray/ctor]. Must have a real-valued or "generic" [data type][@stdlib/ndarray/dtypes]. Input values are internally converted to double-precision floating-point format for computation.
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- **options**: function options (_optional_).
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The function accepts the following options:
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- **dims**: list of dimensions along which to compute the mean. If not provided, the function computes the mean over all elements in the input [ndarray][@stdlib/ndarray/ctor].
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- **dtype**: output ndarray [data type][@stdlib/ndarray/dtypes]. Must be a real-valued floating-point or "generic" [data type][@stdlib/ndarray/dtypes]. Default: `'float64'`.
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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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By default, the function computes the mean over all elements in the input [ndarray][@stdlib/ndarray/ctor]. To compute the mean along specific dimensions, provide a `dims` option.
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```javascript
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var ndarray2array = require( '@stdlib/ndarray/to-array' );
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var array = require( '@stdlib/ndarray/array' );
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var x = array( [ 1.0, 2.0, -2.0, 4.0 ], {
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'shape': [ 2, 2 ],
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'order': 'row-major'
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});
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var v = ndarray2array( x );
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// returns [ [ 1.0, 2.0 ], [ -2.0, 4.0 ] ]
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var y = dmean( x, {
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'dims': [ 0 ]
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});
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// returns <ndarray>
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v = ndarray2array( y );
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// returns [ -0.5, 3.0 ]
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y = dmean( x, {
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'dims': [ 1 ]
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});
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// returns <ndarray>
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v = ndarray2array( y );
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// returns [ 1.5, 1.0 ]
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y = dmean( x, {
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'dims': [ 0, 1 ]
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});
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// returns <ndarray>
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v = y.get();
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// returns 1.25
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```
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By default, the function excludes reduced dimensions from the output [ndarray][@stdlib/ndarray/ctor]. To include the reduced dimensions as singleton dimensions, set the `keepdims` option to `true`.
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```javascript
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var ndarray2array = require( '@stdlib/ndarray/to-array' );
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var array = require( '@stdlib/ndarray/array' );
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var x = array( [ 1.0, 2.0, -2.0, 4.0 ], {
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'shape': [ 2, 2 ],
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'order': 'row-major'
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});
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var v = ndarray2array( x );
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// returns [ [ 1.0, 2.0 ], [ -2.0, 4.0 ] ]
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var y = dmean( x, {
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'dims': [ 0 ],
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'keepdims': true
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});
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// returns <ndarray>
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v = ndarray2array( y );
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// returns [ [ -0.5, 3.0 ] ]
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y = dmean( x, {
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'dims': [ 1 ],
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'keepdims': true
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});
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// returns <ndarray>
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v = ndarray2array( y );
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// returns [ [ 1.5 ], [ 1.0 ] ]
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y = dmean( x, {
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'dims': [ 0, 1 ],
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'keepdims': true
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});
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// returns <ndarray>
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v = ndarray2array( y );
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// returns [ [ 1.25 ] ]
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```
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By default, the function returns an [ndarray][@stdlib/ndarray/ctor] having a `'float64'` [data type][@stdlib/ndarray/dtypes]. To override the default behavior, set the `dtype` option.
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```javascript
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var getDType = require( '@stdlib/ndarray/dtype' );
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var array = require( '@stdlib/ndarray/array' );
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var x = array( [ 1.0, 2.0, -2.0, 4.0 ], {
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'dtype': 'generic'
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});
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var y = dmean( x, {
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'dtype': 'float64'
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});
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// returns <ndarray>
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var dt = String( getDType( y ) );
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// returns 'float64'
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```
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#### dmean.assign( x, out\[, options] )
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Computes the [arithmetic mean][arithmetic-mean] of a double-precision floating-point [ndarray][@stdlib/ndarray/ctor] along one or more 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 zeros = require( '@stdlib/ndarray/zeros' );
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var x = array( [ 1.0, 2.0, -2.0, 4.0 ] );
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var y = zeros( [] );
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var out = dmean.assign( x, y );
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// returns <ndarray>
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var v = out.get();
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// returns 1.25
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var bool = ( out === y );
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// returns true
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```
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The method has the following parameters:
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- **x**: input [ndarray][@stdlib/ndarray/ctor]. Must have a real-valued or generic [data type][@stdlib/ndarray/dtypes].
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- **out**: output [ndarray][@stdlib/ndarray/ctor].
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- **options**: function options (_optional_).
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The method accepts the following options:
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- **dims**: list of dimensions along which to compute the mean. If not provided, the function computes the mean over all elements in the input [ndarray][@stdlib/ndarray/ctor].
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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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- The function performs double-precision floating-point arithmetic internally, regardless of the input array's data type. Input values are converted to `float64` format for computation, ensuring consistent precision across different input types.
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- If any element in the input array is `NaN`, the computed mean for the corresponding reduction will be `NaN`.
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- For empty arrays or reductions over dimensions with zero elements, the function returns `NaN`.
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- Setting the `keepdims` option to `true` can be useful when wanting to ensure that the output [ndarray][@stdlib/ndarray/ctor] is [broadcast-compatible][@stdlib/ndarray/base/broadcast-shapes] with ndarrays having the same shape as the input [ndarray][@stdlib/ndarray/ctor].
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- The output [ndarray][@stdlib/ndarray/ctor] for the main function defaults to `'float64'` data type to preserve the precision of the double-precision computation. For the `assign` method, the output [ndarray][@stdlib/ndarray/ctor] data type is determined by the provided output array.
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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 discreteUniform = require( '@stdlib/random/array/discrete-uniform' );
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var getDType = require( '@stdlib/ndarray/dtype' );
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var ndarray2array = require( '@stdlib/ndarray/to-array' );
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var ndarray = require( '@stdlib/ndarray/ctor' );
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var dmean = require( '@stdlib/stats/dmean' );
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// Generate an array of random numbers:
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var xbuf = discreteUniform( 25, 0, 20, {
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'dtype': 'generic'
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});
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// Wrap in an ndarray:
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var x = new ndarray( 'generic', xbuf, [ 5, 5 ], [ 5, 1 ], 0, 'row-major' );
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console.log( ndarray2array( x ) );
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// Perform a reduction:
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var y = dmean( x, {
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'dims': [ 0 ]
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});
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// Resolve the output array data type:
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var dt = getDType( y );
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console.log( dt );
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// Print the results:
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console.log( ndarray2array( y ) );
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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 for all links. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->
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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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[@stdlib/ndarray/output-dtype-policies]: https://github.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/ndarray/output-dtype-policies
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[@stdlib/ndarray/base/broadcast-shapes]: https://github.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/ndarray/base/broadcast-shapes
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[arithmetic-mean]: https://en.wikipedia.org/wiki/Arithmetic_mean
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</section>
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<!-- /.links -->

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