182 lines
4.8 KiB
Markdown
182 lines
4.8 KiB
Markdown
<!--
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@license Apache-2.0
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Copyright (c) 2018 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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# ranks
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> Compute ranks for values of an array-like object.
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<section class="usage">
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## Usage
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```javascript
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var ranks = require( '@stdlib/stats/ranks' );
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```
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#### ranks( arr\[, opts] )
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Returns the sample ranks of the elements in `arr`, which can be either an [`array`][mdn-array] or [`typed array`][mdn-typed-array].
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```javascript
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var arr = [ 1.1, 2.0, 3.5, 0.0, 2.4 ];
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var out = ranks( arr );
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// returns [ 2, 3, 5, 1, 4 ]
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// Ties are averaged:
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arr = [ 2, 2, 1, 4, 3 ];
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out = ranks( arr );
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// returns [ 2.5, 2.5, 1, 5, 4 ];
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// Missing values are placed last:
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arr = [ null, 2, 2, 1, 4, 3, NaN, NaN ];
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out = ranks( arr );
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// returns [ 6, 2.5, 2.5, 1, 5, 4, 7 ,8 ]
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```
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The function accepts the following options:
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- **method**: `string` indicating how ties are handled. Can be one of the following values: `'average'`, `'min'`, `'max'`, `'ordinal'` and `'dense'`. Default: `'average'`.
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- **missing**: `string` specifying how missing values are handled. Must be either `'last'`, `'first'` or `'remove'`. Default: `'last'`.
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- **encoding**: `array` holding all values which will be regarded as missing values. Default: `[ NaN, null]`.
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When all elements of the `array` are different, the ranks are uniquely determined. When there are equal elements (called _ties_), the `method` option determines how they are handled. The default, `'average'`, replace the ranks of the ties by their mean. Other possible options are `'min'` and `'max'`, which replace the ranks of the ties by their minimum and maximum, respectively. `'dense'` works like `'min'`, with the difference that the next highest element after a tie is assigned the next smallest integer. Finally, `ordinal` gives each element in `arr` a distinct rank, according to the position they appear in.
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```javascript
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var data = [ 2, 2, 1, 4, 3 ];
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// Max method:
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var out = ranks( data, {
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'method': 'max'
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});
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// returns [ 3, 3, 1, 5, 4 ]
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// Min method:
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out = ranks( data, {
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'method': 'min'
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});
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// returns [ 2, 2, 1, 5, 4 ]
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// Ordinal method
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out = ranks( data, {
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'method': 'ordinal'
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});
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// returns [ 2, 3, 1, 5, 4 ]
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// Dense method:
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out = [ 2, 2, 1, 4, 3 ];
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out = ranks( data, {
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'method': 'dense'
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});
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// returns [ 2, 2, 1, 4, 3 ]
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```
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The `missing` option is used to specify how to handle missing data. By default, `NaN` or `null` are treated as missing values. `'last'`specifies that missing values are placed last, `'first'` that the are assigned the lowest ranks and `'remove'` means that they are removed from the array before the ranks are calculated.
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```javascript
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var data = [ NaN, 2, 2, 1, 4, 3, null, null ];
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var out = ranks( data, {
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'missing': 'first'
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});
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// returns [ 1, 5.5, 5.5, 4, 8, 7, 2, 3 ]
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out = ranks( data, {
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'missing': 'last'
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});
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// returns [ 6, 2.5, 2.5, 1, 5, 4, 7 ,8 ]
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out = ranks( data, {
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'missing': 'remove'
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});
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// returns [ 2.5, 2.5, 1, 5, 4 ]
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```
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Custom encoding for missing values is supported via the `encoding` option, which allows to supply the function with an `array` of values which should be treated as missing.
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```javascript
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var Int32Array = require( '@stdlib/array/int32' );
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var data = new Int32Array( [ 2, 1, -999, 3, 4 ] );
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var out = ranks( data, {
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'encoding': [ -999 ]
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});
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// returns [ 2, 1, 5, 3, 4 ]
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```
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</section>
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<!-- /.usage -->
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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 Int32Array = require( '@stdlib/array/int32' );
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var round = require( '@stdlib/math/base/special/round' );
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var randu = require( '@stdlib/random/base/randu' );
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var ranks = require( '@stdlib/stats/ranks' );
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var data;
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var out;
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var i;
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// Plain arrays...
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data = new Array( 10 );
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for ( i = 0; i < data.length; i++ ) {
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data[ i ] = round( randu()*10.0 );
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}
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out = ranks( data );
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// returns <array>
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// Typed arrays...
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data = new Int32Array( 10 );
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for ( i = 0; i < data.length; i++ ) {
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data[ i ] = randu() * 10.0;
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}
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out = ranks( data );
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// returns <array>
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```
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</section>
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<!-- /.examples -->
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<section class="references">
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</section>
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<!-- /.references -->
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<section class="links">
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[mdn-array]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array
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[mdn-typed-array]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Typed_arrays
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</section>
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<!-- /.links -->
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