84 lines
2.5 KiB
JavaScript
84 lines
2.5 KiB
JavaScript
/**
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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 isCollection = require( '@stdlib/assert/is-collection' );
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var isFunction = require( '@stdlib/assert/is-function' );
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// MAIN //
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/**
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* Applies a function against an accumulator and each element in a collection and returns the accumulated result, iterating from right to left.
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*
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* ## Notes
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*
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* - For dynamic array resizing, the only behavior made intentionally consistent with `reduce` (iterating from left to right) is when elements are pushed onto the beginning (end) of an array. In other words, for `reduce()`, `[].push()` behavior is consistent with `reduceRight()` `[].unshift()` behavior.
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*
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*
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* @param {Collection} collection - input collection
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* @param {*} initial - initial value
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* @param {Function} reducer - reduction function
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* @param {*} [thisArg] - reduction function execution context
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* @throws {TypeError} first argument must be a collection
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* @throws {TypeError} third argument must be a function
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* @returns {*} accumulated result
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*
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* @example
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* function sum( acc, value, index ) {
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* console.log( '%s: %d', index, value );
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* return acc + value;
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* }
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*
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* var arr = [ 1, 2, 3, 4 ];
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*
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* var s = reduceRight( arr, 0, sum );
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* // returns 10
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*/
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function reduceRight( collection, initial, reducer, thisArg ) {
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var len;
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var acc;
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var i;
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if ( !isCollection( collection ) ) {
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throw new TypeError( 'invalid argument. First argument must be a collection. Value: `'+collection+'`.' );
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}
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if ( !isFunction( reducer ) ) {
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throw new TypeError( 'invalid argument. Third argument must be a function. Value:`'+reducer+'`.' );
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}
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len = collection.length;
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acc = initial;
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for ( i = len-1; i >= 0; i-- ) {
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acc = reducer.call( thisArg, acc, collection[ i ], i, collection );
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// Account for dynamically resizing a collection...
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if ( len !== collection.length ) {
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i += ( collection.length - len );
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len = collection.length;
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}
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}
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return acc;
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}
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// EXPORTS //
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module.exports = reduceRight;
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