96 lines
2.5 KiB
JavaScript
96 lines
2.5 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 isCollection = require( '@stdlib/assert/is-collection' );
|
||
|
|
var isFunction = require( '@stdlib/assert/is-function' );
|
||
|
|
var hasOwnProp = require( '@stdlib/assert/has-own-property' );
|
||
|
|
var validate = require( './validate.js' );
|
||
|
|
|
||
|
|
|
||
|
|
// MAIN //
|
||
|
|
|
||
|
|
/**
|
||
|
|
* Groups values according to an indicator function and returns group counts.
|
||
|
|
*
|
||
|
|
* @param {Collection} collection - input collection
|
||
|
|
* @param {Options} [options] - function options
|
||
|
|
* @param {*} [options.thisArg] - execution context
|
||
|
|
* @param {Function} indicator - indicator function specifying which group an element in the input collection belongs to
|
||
|
|
* @throws {TypeError} first argument must be a collection
|
||
|
|
* @throws {TypeError} options argument must be an object
|
||
|
|
* @throws {TypeError} last argument must be a function
|
||
|
|
* @throws {TypeError} must provide valid options
|
||
|
|
* @returns {Object} counts
|
||
|
|
*
|
||
|
|
* @example
|
||
|
|
* function indicator( v ) {
|
||
|
|
* return v[ 0 ];
|
||
|
|
* }
|
||
|
|
* var arr = [ 'beep', 'boop', 'foo', 'bar' ];
|
||
|
|
*
|
||
|
|
* var out = countBy( arr, indicator );
|
||
|
|
* // returns { 'b': 3, 'f': 1 }
|
||
|
|
*/
|
||
|
|
function countBy( collection, options, indicator ) {
|
||
|
|
var thisArg;
|
||
|
|
var opts;
|
||
|
|
var err;
|
||
|
|
var out;
|
||
|
|
var len;
|
||
|
|
var cb;
|
||
|
|
var g;
|
||
|
|
var i;
|
||
|
|
if ( !isCollection( collection ) ) {
|
||
|
|
throw new TypeError( 'invalid argument. First argument must be a collection. Value: `'+collection+'`.' );
|
||
|
|
}
|
||
|
|
opts = {};
|
||
|
|
if ( arguments.length === 2 ) {
|
||
|
|
cb = options;
|
||
|
|
} else {
|
||
|
|
err = validate( opts, options );
|
||
|
|
if ( err ) {
|
||
|
|
throw err;
|
||
|
|
}
|
||
|
|
cb = indicator;
|
||
|
|
}
|
||
|
|
if ( !isFunction( cb ) ) {
|
||
|
|
throw new TypeError( 'invalid argument. Last argument must be a function. Value: `'+cb+'`.' );
|
||
|
|
}
|
||
|
|
thisArg = opts.thisArg;
|
||
|
|
len = collection.length;
|
||
|
|
out = {};
|
||
|
|
for ( i = 0; i < len; i++ ) {
|
||
|
|
g = cb.call( thisArg, collection[ i ], i );
|
||
|
|
if ( hasOwnProp( out, g ) ) {
|
||
|
|
out[ g ] += 1;
|
||
|
|
} else {
|
||
|
|
out[ g ] = 1;
|
||
|
|
}
|
||
|
|
}
|
||
|
|
return out;
|
||
|
|
}
|
||
|
|
|
||
|
|
|
||
|
|
// EXPORTS //
|
||
|
|
|
||
|
|
module.exports = countBy;
|