// wink-nlp-utils
// NLP Functions for amplifying negations, managing elisions,
// creating ngrams, stems, phonetic codes to tokens and more.
//
// Copyright (C) GRAYPE Systems Private Limited
//
// This file is part of “wink-nlp-utils”.
//
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// copy of this software and associated documentation files (the "Software"),
// to deal in the Software without restriction, including without limitation
// the rights to use, copy, modify, merge, publish, distribute, sublicense,
// and/or sell copies of the Software, and to permit persons to whom the
// Software is furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included
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//
// ## string
// ### setOfNGrams
/**
*
* Generates the set of ngrams of `size` from the input string. The
* default size is 2, which means it will generate set of bigrams by default.
* It also has an alias **`song()`**.
*
* @alias string#setOfNGrams
* @param {string} str the input string.
* @param {number} [size=2] ngram size.
* @param {function} [ifn=undefined] a function to build index; it is called for
* every **unique occurrence of ngram** of `str`; and it receives the ngram and the `idx`
* as input arguments. The `build()` function of [helper.returnIndexer](#helperreturnindexer)
* may be used as `ifn`. If `undefined` then index is not built.
* @param {number} [idx=undefined] the index; passed as the second argument to the `ifn`
* function.
* @return {set} of ngrams of `size` of `str`.
* @example
* setOfNGrams( 'mama' );
* // -> Set { 'ma', 'am' }
* song( 'mamma' );
* // -> Set { 'ma', 'am', 'mm' }
*/
var setOfNGrams = function ( str, size, ifn, idx ) {
var ng = ( size || 2 ),
ngSet = new Set(),
tg;
for ( var i = 0, imax = str.length; i < imax; i += 1 ) {
tg = str.slice( i, i + ng );
if ( tg.length === ng ) {
if ( ( typeof ifn === 'function' ) && !ngSet.has( tg ) ) {
ifn( tg, idx );
}
ngSet.add( tg );
}
}
return ( ngSet );
}; // song()
module.exports = setOfNGrams;