time-to-botec

README.md (7414B)

---

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 # Sample
 
 > Sample elements from an array-like object.
 
 <section class="intro">
 
 </section>
 
 <!-- /.intro -->
 
 <section class="usage">
 
 ## Usage
 
 ```javascript
 var sample = require( '@stdlib/random/sample' );
 ```
 
 #### sample( x\[, options] )
 
 Samples elements from an `array`-like object. By default, elements are drawn with replacement from `x` to create an output `array` having the same length as `x`.
 
 ```javascript
 var out = sample( [ 'a', 'b', 'c' ] );
 // e.g., returns [ 'a', 'a', 'b' ]
 
 out = sample( [ 3, 6, 9 ] );
 // e.g., returns [ 3, 9, 6 ]
 
 var bool = ( out.length === 3 );
 // returns true
 ```
 
 The function accepts the following `options`:
 
 -   **size**: sample size. Default: `N = x.length`.
 -   **probs**: a probability `array`. Default: `[1/N,...,1/N]`.
 -   **replace**: `boolean` indicating whether to sample from `x` with replacement. Default: `true`.
 
 By default, the function returns an `array` having the same length as `x`. To generate a sample of a different size, set the `size` option.
 
 ```javascript
 var out = sample( [ 3, 6, 9 ], {
     'size': 10
 });
 // e.g., returns [ 6, 3, 9, 9, 9, 6, 9, 6, 9, 3 ]
 
 out = sample( [ 0, 1 ], {
     'size': 20
 });
 // e.g., returns [ 0, 0, 0, 1, 1, 0, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 1, 1, 1, 0 ]
 ```
 
 To draw a sample _without_ replacement, set the `replace` option to `false`. In this case, the `size` option cannot be an integer larger than the number of elements in `x`.
 
 ```javascript
 var out = sample( [ 1, 2, 3, 4, 5, 6 ], {
     'replace': false,
     'size': 3
 });
 // e.g., returns [ 6, 1, 5 ]
 
 out = sample( [ 0, 1 ], {
     'replace': false
 });
 // e.g., returns [ 0, 1 ]
 ```
 
 By default, the probability of sampling an element is the same for all elements. To assign elements different probabilities, set the `probs` option.
 
 ```javascript
 var x = [ 1, 2, 3, 4, 5, 6 ];
 var out = sample( x, {
     'probs': [ 0.1, 0.1, 0.1, 0.1, 0.1, 0.5 ]
 });
 // e.g., returns [ 5, 6, 6, 5, 6, 4 ]
 
 x = [ 1, 2, 3, 4, 5, 6 ];
 out = sample( x, {
     'probs': [ 0.1, 0.1, 0.1, 0.1, 0.1, 0.5 ],
     'size': 3,
     'replace': false
 });
 // e.g., returns [ 6, 4, 1 ]
 ```
 
 The `probs` option **must** be a numeric array consisting of nonnegative values which sum to one. When sampling _without_ replacement, note that the `probs` option denotes the initial element probabilities which are then updated after each draw.
 
 #### sample.factory( \[pool, ]\[options] )
 
 Returns a `function` to sample elements from an `array`-like object. 
 
 ```javascript
 var mysample = sample.factory();
 
 var out = mysample( [ 0, 1, 2, 3, 4 ] );
 // e.g., returns [ 4, 3, 4, 4 ]
 ```
 
 If provided an array-like object `pool`, the returned function will always sample from the supplied object.
 
 ```javascript
 var mysample = sample.factory( [ 1, 2, 3, 4, 5, 6 ] );
 
 var out = mysample();
 // e.g., returns [ 2, 4, 1, 6, 5, 1 ]
 
 out = mysample();
 // e.g., returns [ 5, 2, 3, 6, 1, 4 ]
 ```
 
 The function accepts the following `options`:
 
 -   **seed**: pseudorandom number generator seed.
 -   **size**: sample size.
 -   **mutate**: `boolean` indicating whether to mutate the `pool` when sampling without replacement. Default: `false`.
 -   **replace**: `boolean` indicating whether to sample with replacement. Default: `true`.
 
 To seed the pseudorandom number generator, set the `seed` option.
 
 ```javascript
 var mysample = sample.factory({
     'seed': 430
 });
 
 var out = mysample( [ 1, 2, 3, 4, 5, 6 ] );
 // e.g., returns [ 1, 1, 1, 5, 4, 4 ]
 
 mysample = sample.factory( [ 1, 2, 3, 4, 5, 6 ], {
     'seed': 430
 });
 
 out = mysample();
 // e.g., returns [ 1, 1, 1, 5, 4, 4 ]
 ```
 
 To specify a sample size and/or override the default sample size, set the `size` option.
 
 ```javascript
 var mysample = sample.factory({
     'size': 4
 });
 
 var out = mysample( [ 0, 1 ] );
 // e.g., returns [ 0, 0, 0, 1 ]
 
 // Override the size option...
 out = mysample( [ 0, 1 ], {
     'size': 1
 });
 // e.g., returns [ 1 ]
 ```
 
 By default, the returned function draws samples _with_ replacement. To override the default `replace` strategy, set the `replace` option.
 
 ```javascript
 var mysample = sample.factory({
     'replace': false
 });
 
 var out = mysample( [ 1, 2, 3 ] );
 // e.g., returns [ 3, 1, 2 ]
 ```
 
 If a population from which to sample is provided, the underlying `pool` remains constant for each function invocation. To mutate the `pool` by permanently removing observations when sampling _without_ replacement, set the `mutate` option.
 
 ```javascript
 var mysample = sample.factory( [ 1, 2, 3, 4, 5, 6 ], {
     'mutate': true,
     'replace': false,
     'size': 3,
     'seed': 342
 });
 
 var out = mysample();
 // e.g., returns [ 6, 5, 3 ]
 
 // Override the mutate option...
 out = mysample({
     'mutate': false
 });
 // e.g., returns [ 1, 2, 4 ]
 
 out = mysample();
 // e.g., returns [ 1, 2, 4 ]
 ```
 
 The returned function returns `null` after all population units are exhausted.
 
 ```javascript
 var mysample = sample.factory( [ 1, 2, 3, 4, 5, 6 ], {
     'mutate': true,
     'replace': false
 });
 
 var out = mysample();
 // e.g., returns [ 3, 2, 1, 6, 5, 4 ]
 
 out = mysample();
 // returns null
 ```
 
 </section>
 
 <!-- /.usage -->
 
 <section class="examples">
 
 ## Examples
 
 <!-- eslint no-undef: "error" -->
 
 ```javascript
 var sample = require( '@stdlib/random/sample' );
 
 var out;
 var x;
 
 // By default, sample uniformly with replacement:
 x = [ 'a', 'b', 'c', 'd' ];
 out = sample( x, {
     'size': 10
 });
 // e.g., returns [ 'd', 'c', 'b', 'b', 'b', 'd', 'c', 'c', 'b', 'd' ]
 
 // Sample with replacement with custom probabilities:
 x = [ 'a', 'b', 'c', 'd' ];
 out = sample( x, {
     'probs': [ 0.1, 0.1, 0.2, 0.6 ],
     'size': 10
 });
 // e.g., returns [ 'b', 'a', 'c', 'd', 'd', 'd', 'd', 'c', 'd', 'd' ]
 
 // Sample without replacement:
 x = [ 'a', 'b', 'c', 'd' ];
 out = sample( x, {
     'size': 3,
     'replace': false
 });
 // e.g., returns [ 'd', 'c', 'a' ]
 
 // Sample without replacement when (initial) probabilities are nonuniform:
 x = [ 1, 2, 3, 4, 5, 6 ];
 out = sample( x, {
     'probs': [ 0.1, 0.1, 0.1, 0.1, 0.1, 0.5 ],
     'size': 3,
     'replace': false
 });
 // e.g., returns [ 2, 3, 6 ]
 ```
 
 </section>
 
 <!-- /.examples -->
 
 <!-- Section to include cited references. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->
 
 <section class="references">
 
 ### References
 
 -   Knuth, Donald E. 1997. _The Art of Computer Programming, Volume 2 (3rd Ed.): Seminumerical Algorithms_. Boston, MA, USA: Addison-Wesley Longman Publishing Co., Inc.
 -   Vose, Michael D. 1991. "A linear algorithm for generating random numbers with a given distribution." _IEEE Transactions on Software Engineering_ 17 (9): 972–75. doi:[10.1109/32.92917][@vose:1991].
 
 </section>
 
 <!-- /.references -->
 
 <section class="links">
 
 [@vose:1991]: https://doi.org/10.1109/32.92917
 
 </section>
 
 <!-- /.links -->