71 lines
1.7 KiB
JavaScript
71 lines
1.7 KiB
JavaScript
/**
|
|
* @license Apache-2.0
|
|
*
|
|
* Copyright (c) 2018 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 floor = require( '@stdlib/math/base/special/floor' );
|
|
|
|
|
|
// FUNCTIONS //
|
|
|
|
var slice = Array.prototype.slice;
|
|
|
|
|
|
// MAIN //
|
|
|
|
/**
|
|
* Samples uniformly without replacement using the Fisher-Yates shuffle.
|
|
*
|
|
* ## 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.
|
|
*
|
|
* @private
|
|
* @param {ArrayLike} x - array-like object from which to sample
|
|
* @param {NonNegativeInteger} size - sample size
|
|
* @param {Function} rand - PRNG for generating uniformly distributed numbers
|
|
* @returns {Array} sample
|
|
*/
|
|
function fisherYates( x, size, rand ) {
|
|
var tmp;
|
|
var N;
|
|
var i;
|
|
var j;
|
|
|
|
N = x.length;
|
|
|
|
// Note: we skip the first element, as no further swaps are possible given that all other indices are excluded from swapping...
|
|
for ( i = N-1; i > 0; i-- ) {
|
|
// Generate an integer index on the interval: [0,i]
|
|
j = floor( rand()*(i+1) );
|
|
|
|
// Swap elements:
|
|
tmp = x[ i ];
|
|
x[ i ] = x[ j ];
|
|
x[ j ] = tmp;
|
|
}
|
|
return slice.call( x, 0, size );
|
|
}
|
|
|
|
|
|
// EXPORTS //
|
|
|
|
module.exports = fisherYates;
|