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* @license Apache-2.0
*
* Copyright (c) 2019 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 setReadOnly = require( '@stdlib/utils/define-nonenumerable-read-only-property' );
var isFunction = require( '@stdlib/assert/is-function' );
var isIteratorLike = require( '@stdlib/assert/is-iterator-like' );
var iteratorSymbol = require( '@stdlib/symbol/iterator' );
var format = require( '@stdlib/string/format' );
// FUNCTIONS //
/**
* Tests if a value is unique according to a predicate function when compared to a list of values.
*
* @private
* @param {Array} arr - input array
* @param {*} v - test value
* @param {Function} predicate - predicate function
* @param {*} thisArg - execution context
* @returns {boolean} boolean indicating whether a value is "unique"
*
* @example
* function predicate( a, b ) {
* return ( a !== b );
* }
*
* var bool = isUnique( [ 1, 2, 3 ], 1, predicate, null );
* // returns false
*
* bool = isUnique( [ 1, 2, 3 ], 4, predicate, null );
* // returns true
*/
function isUnique( arr, v, predicate, thisArg ) {
var len;
var i;
len = arr.length;
for ( i = 0; i < len; i++ ) {
if ( !predicate.call( thisArg, arr[ i ], v ) ) {
return false;
}
}
return true;
}
// MAIN //
/**
* Returns an iterator which returns unique values according to a predicate function.
*
* @param {Iterator} iterator - input iterator
* @param {Function} predicate - predicate function
* @param {*} [thisArg] - execution context
* @throws {TypeError} first argument must be an iterator protocol-compliant object
* @throws {TypeError} second argument must be a function
* @returns {Iterator} iterator
*
* @example
* var array2iterator = require( '@stdlib/array/to-iterator' );
*
* function predicate( a, b ) {
* return ( a !== b );
* }
*
* var iter = iterUniqueBy( array2iterator( [ 1, 2, 1, 2, 4 ] ), predicate );
*
* var v = iter.next().value;
* // returns 1
*
* v = iter.next().value;
* // returns 2
*
* v = iter.next().value;
* // returns 4
*
* var bool = iter.next().done;
* // returns true
*/
function iterUniqueBy( iterator, predicate, thisArg ) {
var iter;
var hash;
var FLG;
if ( !isIteratorLike( iterator ) ) {
throw new TypeError( format( 'invalid argument. First argument must be an iterator protocol-compliant object. Value: `%s`.', iterator ) );
}
if ( !isFunction( predicate ) ) {
throw new TypeError( format( 'invalid argument. Second argument must be a function. Value: `%s`.', predicate ) );
}
hash = [];
// Create an iterator protocol-compliant object:
iter = {};
setReadOnly( iter, 'next', next );
setReadOnly( iter, 'return', end );
// If an environment supports `Symbol.iterator`, make the iterator iterable:
if ( iteratorSymbol && isFunction( iterator[ iteratorSymbol ] ) ) {
setReadOnly( iter, iteratorSymbol, factory );
}
return iter;
/**
* Returns an iterator protocol-compliant object containing the next iterated value.
*
* @private
* @returns {Object} iterator protocol-compliant object
*/
function next() {
var v;
if ( FLG ) {
return {
'done': true
};
}
while ( true ) {
v = iterator.next();
if ( v.done ) {
FLG = true;
return v;
}
v = v.value;
if ( isUnique( hash, v, predicate, thisArg ) ) {
hash.push( v );
break;
}
}
return {
'value': v,
'done': false
};
}
/**
* Finishes an iterator.
*
* @private
* @param {*} [value] - value to return
* @returns {Object} iterator protocol-compliant object
*/
function end( value ) {
FLG = true;
if ( arguments.length ) {
return {
'value': value,
'done': true
};
}
return {
'done': true
};
}
/**
* Returns a new iterator.
*
* @private
* @returns {Iterator} iterator
*/
function factory() {
return iterUniqueBy( iterator[ iteratorSymbol ](), predicate, thisArg );
}
}
// EXPORTS //
module.exports = iterUniqueBy;
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