91 lines
2.2 KiB
JavaScript
91 lines
2.2 KiB
JavaScript
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/**
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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 indexOf = require( './../../index-of' );
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// MAIN //
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/**
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* Generates a frequency table.
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*
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* ## Notes
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*
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* - The output is an array of arrays. Each sub-array corresponds to a unique value in the input collection and is structured as follows:
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*
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* - 0: unique value
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* - 1: value count
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* - 2: frequency percentage
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*
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*
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* @param {Collection} collection - input collection
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* @throws {TypeError} first argument must be a collection
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* @returns {(Array<Array>|Array)} frequency table
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*
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* @example
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* var arr = [ 'beep', 'boop', 'foo', 'beep' ];
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*
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* var out = tabulate( arr );
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* // returns [ [ 'beep', 2, 0.5 ], [ 'boop', 1, 0.25 ], [ 'foo', 1, 0.25 ] ]
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*/
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function tabulate( collection ) {
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var count;
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var tmp;
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var len;
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var out;
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var v;
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var i;
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var j;
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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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count = 0;
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tmp = [];
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out = [];
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// 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.
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len = collection.length;
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for ( i = 0; i < len; i++ ) {
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v = collection[ i ];
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count += 1;
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j = indexOf( tmp, v );
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if ( j === -1 ) {
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tmp.push( v );
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out.push( [ v, 1, 0 ] );
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} else {
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out[ j ][ 1 ] += 1;
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}
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}
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// Compute percentages...
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len = out.length;
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for ( i = 0; i < len; i++ ) {
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out[ i ][ 2 ] = out[ i ][ 1 ] / count;
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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 = tabulate;
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