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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';
// VARIABLES //
var SORT_OPTS = {
'numeric': true // Use numeric collation such that "1" < "2" < "10"...
};
// FUNCTIONS //
/**
* Comparator function to sort values in ascending order.
*
* @private
* @param {*} a - first value
* @param {*} b - second value
* @returns {number} negative number if `a` comes before `b, positive if `a` comes after `b`, and `0` if they are equivalent
*/
function ascending( a, b ) {
return String( a ).localeCompare( String( b ), void 0, SORT_OPTS );
}
// MAIN //
/**
* Returns the unique elements in an array.
*
* @private
* @param {Array} arr - input array
* @returns {Array} array of unique elements
*/
function unique( arr ) {
var len;
var out;
var val;
var i;
var j;
// Copy the array to avoid mutation:
out = Array.prototype.slice.call( arr );
len = out.length;
// Sort array in ascending order:
out.sort( ascending );
// Loop through the array, only incrementing a pointer when successive values are different. When a succeeding value is different, move the pointer and set the next value. In the trivial case where all array elements are unique, we incur a slight penalty in resetting the element value for each unique value. In other cases, we simply move a unique value to a new position in the array. The end result is a sorted array with unique values.
for ( i = 1, j = 0; i < len; i++ ) {
val = out[ i ];
if ( out[ j ] !== val ) {
j += 1;
out[ j ] = val;
}
}
// Truncate the array:
out.length = j+1;
return out;
}
// EXPORTS //
module.exports = unique;
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