77 lines
2.1 KiB
JavaScript
77 lines
2.1 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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* Converts a collection to an object whose keys are determined by a provided function and whose values are the collection values.
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*
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* @param {Collection} collection - input collection
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* @param {Function} fcn - function to invoke
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* @param {*} [thisArg] - execution context
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* @throws {TypeError} first argument must be an object
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* @throws {TypeError} second argument must be a function
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* @returns {Object} output object
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*
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* @example
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* function toKey( value, index ) {
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* console.log( '%d: %s', index, JSON.stringify( value ) );
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* return value.name;
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* }
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*
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* var collection = [
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* { 'name': 'beep', 'a': 1 },
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* { 'name': 'boop', 'b': 2 }
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* ];
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*
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* var obj = keyBy( collection, toKey );
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* // returns { 'beep': { 'name': 'beep', 'a': 1 }, 'boop': { 'name': 'boop', 'b': 2 } }
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*/
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function keyBy( collection, fcn, thisArg ) {
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var out;
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var len;
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var key;
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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( fcn ) ) {
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throw new TypeError( 'invalid argument. Second argument must be a function. Value: `'+fcn+'`.' );
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}
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len = collection.length;
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out = {};
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for ( i = 0; i < len; i++ ) {
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key = fcn.call( thisArg, collection[ i ], i );
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out[ key ] = collection[ i ];
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}
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return out;
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}
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// EXPORTS //
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module.exports = keyBy;
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