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* @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 hasOwnProp = require( '@stdlib/assert/has-own-property' );
// MAIN //
/**
* Groups values according to an indicator function and outputs results as object values.
*
* ## Notes
*
* - We need to cache the object value to prevent the edge case where, during the invocation of the indicator function, the value at key `k` is swapped for some other value. For some, that might be a feature; here, we take the stance that one should be less clever.
*
* @private
* @param {(Object|Array|TypedArray)} obj - input object
* @param {Options} opts - function options
* @param {*} [opts.thisArg] - execution context
* @param {Function} indicator - indicator function indicating which group an element in the input object belongs to
* @returns {Object} results
*
* @example
* function indicator( v ) {
* return v[ 0 ];
* }
*
* function Foo() {
* this.a = 'beep';
* this.b = 'boop';
* return this;
* }
*
* Foo.prototype = Object.create( null );
* Foo.prototype.c = 'foo';
* Foo.prototype.d = 'bar';
*
* var obj = new Foo();
*
* var out = groupIn( obj, {}, indicator );
* // e.g., returns { 'b': [ 'beep', 'boop', 'bar' ], 'f': [ 'foo' ] }
*/
function groupIn( obj, opts, indicator ) {
var thisArg;
var out;
var key;
var v;
var g;
thisArg = opts.thisArg;
out = {};
for ( key in obj ) { // eslint-disable-line guard-for-in
v = obj[ key ];
g = indicator.call( thisArg, v, key );
if ( hasOwnProp( out, g ) ) {
out[ g ].push( v );
} else {
out[ g ] = [ v ];
}
}
return out;
}
// EXPORTS //
module.exports = groupIn;
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