71 lines
1.7 KiB
JavaScript
71 lines
1.7 KiB
JavaScript
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/**
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* @license Apache-2.0
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*
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* Copyright (c) 2018 The Stdlib Authors.
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*
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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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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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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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'use strict';
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// MODULES //
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var floor = require( '@stdlib/math/base/special/floor' );
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// FUNCTIONS //
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var slice = Array.prototype.slice;
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// MAIN //
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/**
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* Samples uniformly without replacement using the Fisher-Yates shuffle.
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*
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* ## References
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*
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* - Knuth, Donald E. 1997. _The Art of Computer Programming, Volume 2 (3rd Ed.): Seminumerical Algorithms_. Boston, MA, USA: Addison-Wesley Longman Publishing Co., Inc.
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*
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* @private
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* @param {ArrayLike} x - array-like object from which to sample
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* @param {NonNegativeInteger} size - sample size
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* @param {Function} rand - PRNG for generating uniformly distributed numbers
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* @returns {Array} sample
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*/
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function fisherYates( x, size, rand ) {
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var tmp;
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var N;
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var i;
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var j;
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N = x.length;
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// Note: we skip the first element, as no further swaps are possible given that all other indices are excluded from swapping...
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for ( i = N-1; i > 0; i-- ) {
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// Generate an integer index on the interval: [0,i]
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j = floor( rand()*(i+1) );
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// Swap elements:
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tmp = x[ i ];
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x[ i ] = x[ j ];
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x[ j ] = tmp;
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}
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return slice.call( x, 0, size );
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}
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// EXPORTS //
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module.exports = fisherYates;
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