time-to-botec

Benchmark sampling in different programming languages
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tabulate_by.js (3218B)

      1 /**
      2 * @license Apache-2.0
      3 *
      4 * Copyright (c) 2018 The Stdlib Authors.
      5 *
      6 * Licensed under the Apache License, Version 2.0 (the "License");
      7 * you may not use this file except in compliance with the License.
      8 * You may obtain a copy of the License at
      9 *
     10 *    http://www.apache.org/licenses/LICENSE-2.0
     11 *
     12 * Unless required by applicable law or agreed to in writing, software
     13 * distributed under the License is distributed on an "AS IS" BASIS,
     14 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     15 * See the License for the specific language governing permissions and
     16 * limitations under the License.
     17 */
     18 
     19 'use strict';
     20 
     21 // MODULES //
     22 
     23 var isCollection = require( '@stdlib/assert/is-collection' );
     24 var isFunction = require( '@stdlib/assert/is-function' );
     25 var indexOf = require( './../../index-of' );
     26 var validate = require( './validate.js' );
     27 
     28 
     29 // MAIN //
     30 
     31 /**
     32 * Generates a frequency table according to a provided function.
     33 *
     34 * ## Notes
     35 *
     36 * -   The output is an array of arrays. Each sub-array corresponds to a unique value in the input collection and is structured as follows:
     37 *
     38 *     -   0: unique value
     39 *     -   1: value count
     40 *     -   2: frequency percentage
     41 *
     42 *
     43 * @param {Collection} collection - input collection
     44 * @param {Options} [options] - function options
     45 * @param {*} [options.thisArg] - execution context
     46 * @param {Function} indicator - function whose return values are used to populate the output frequency table
     47 * @throws {TypeError} first argument must be a collection
     48 * @throws {TypeError} options argument must be an object
     49 * @throws {TypeError} last argument must be a function
     50 * @throws {TypeError} must provide valid options
     51 * @returns {(Array<Array>|Array)} frequency table
     52 *
     53 * @example
     54 * function indicator( value ) {
     55 *     return value[ 0 ];
     56 * }
     57 *
     58 * var arr = [ 'beep', 'boop', 'foo', 'beep' ];
     59 *
     60 * var out = tabulateBy( arr, indicator );
     61 * // returns [ [ 'b', 3, 0.75 ], [ 'f', 1, 0.25 ] ]
     62 */
     63 function tabulateBy( collection, options, indicator ) {
     64 	var thisArg;
     65 	var count;
     66 	var opts;
     67 	var tmp;
     68 	var len;
     69 	var out;
     70 	var err;
     71 	var cb;
     72 	var v;
     73 	var i;
     74 	var j;
     75 	if ( !isCollection( collection ) ) {
     76 		throw new TypeError( 'invalid argument. First argument must be a collection. Value: `'+collection+'`.' );
     77 	}
     78 	opts = {};
     79 	if ( arguments.length === 2 ) {
     80 		cb = options;
     81 	} else {
     82 		err = validate( opts, options );
     83 		if ( err ) {
     84 			throw err;
     85 		}
     86 		cb = indicator;
     87 	}
     88 	if ( !isFunction( cb ) ) {
     89 		throw new TypeError( 'invalid argument. Last argument must be a function. Value: `'+cb+'`.' );
     90 	}
     91 	thisArg = opts.thisArg;
     92 	count = 0;
     93 	tmp = [];
     94 	out = [];
     95 
     96 	// For each collection element, determine if we've seen the element before. If not, cache a reference which points to its location in the output array; otherwise, update the running count.
     97 	len = collection.length;
     98 	for ( i = 0; i < len; i++ ) {
     99 		v = cb.call( thisArg, collection[ i ], i );
    100 		count += 1;
    101 		j = indexOf( tmp, v );
    102 		if ( j === -1 ) {
    103 			tmp.push( v );
    104 			out.push( [ v, 1, 0 ] );
    105 		} else {
    106 			out[ j ][ 1 ] += 1;
    107 		}
    108 	}
    109 	// Compute percentages...
    110 	len = out.length;
    111 	for ( i = 0; i < len; i++ ) {
    112 		out[ i ][ 2 ] = out[ i ][ 1 ] / count;
    113 	}
    114 	return out;
    115 }
    116 
    117 
    118 // EXPORTS //
    119 
    120 module.exports = tabulateBy;