# Yahoo! UI Library

### collection 3.0.0

Yahoo! UI Library > collection > array-extras.js (source view)
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    /**
     * Collection utilities beyond what is provided in the YUI core
     * @module collection
     */

    var L = Y.Lang, Native = Array.prototype, A = Y.Array;

    /**
     * Adds the following array utilities to the YUI instance
     * (Y.Array).  This is in addition to the methods provided
     * in the core.
     * @class YUI~array~extras
     */

    /**
     * Returns the index of the last item in the array
     * that contains the specified value, -1 if the
     * value isn't found.
     * method Array.lastIndexOf
     * @static
     * @param a {Array} the array to search
     * @param val the value to search for
     * @return {int} the index of hte item that contains the value or -1
     */
    A.lastIndexOf = (Native.lastIndexOf) ?
        function(a ,val) {
            return a.lastIndexOf(val);
        } :
        function(a, val) {
            for (var i=a.length-1; i>=0; i=i-1) {
                if (a[i] === val) {
                    break;
                }
            }
            return i;
        };

    /**
     * Returns a copy of the array with the duplicate entries removed
     * @method Array.unique
     * @static
     * @param a {Array} the array to find the subset of uniques for
     * @param sort {bool} flag to denote if the array is sorted or not. Defaults to false, the more general operation
     * @return {Array} a copy of the array with duplicate entries removed
     */
    A.unique = function(a, sort) {
        var b = a.slice(), i = 0, n = -1, item = null;

        while (i < b.length) {
            item = b[i];
            while ((n = b.lastIndexOf(item)) !== i) {
                b.splice(n, 1);
            }
            i += 1;
        }

        // Note: the sort option doesn't really belong here... I think it was added
        // because there was a way to fast path the two operations together.  That
        // implementation was not working, so I replaced it with the following.
        // Leaving it in so that the API doesn't get broken.
        if (sort) {
            if (L.isNumber(b[0])) {
                b.sort(A.numericSort);
            } else {
                b.sort();
            }
        }

        return b;
    };

    /**
    * Executes the supplied function on each item in the array.
    * Returns a new array containing the items that the supplied
    * function returned true for.
    * @method Array.filter
    * @param a {Array} the array to iterate
    * @param f {Function} the function to execute on each item
    * @param o Optional context object
    * @static
    * @return {Array} The items on which the supplied function
    * returned true. If no items matched an empty array is
    * returned.
    */
    A.filter = (Native.filter) ?
        function(a, f, o) {
            return Native.filter.call(a, f, o);
        } :
        function(a, f, o) {
            var results = [];
            A.each(a, function(item, i, a) {
                if (f.call(o, item, i, a)) {
                    results.push(item);
                }
            });

            return results;
        };

    /**
    * The inverse of filter. Executes the supplied function on each item.
    * Returns a new array containing the items that the supplied
    * function returned *false* for.
    * @method Array.reject
    * @param a {Array} the array to iterate
    * @param f {Function} the function to execute on each item
    * @param o Optional context object
    * @static
    * @return {Array} The items on which the supplied function
    * returned false.
    */
    A.reject = function(a, f, o) {
        return A.filter(a, function(item, i, a) {
            return !f.call(o, item, i, a);
        });
    };

    /**
    * Executes the supplied function on each item in the array.
    * @method Array.every
    * @param a {Array} the array to iterate
    * @param f {Function} the function to execute on each item
    * @param o Optional context object
    * @static
    * @return {boolean} true if every item in the array returns true
    * from the supplied function.
    */
    A.every = (Native.every) ?
        function(a, f, o) {
            return Native.every.call(a,f,o);
        } :
        function(a, f, o) {
            var l = a.length;
            for (var i = 0; i < l; i=i+1) {
                if (!f.call(o, a[i], i, a)) {
                    return false;
                }
            }

            return true;
        };

    /**
    * Executes the supplied function on each item in the array.
    * @method Array.map
    * @param a {Array} the array to iterate
    * @param f {Function} the function to execute on each item
    * @param o Optional context object
    * @static
    * @return {Array} A new array containing the return value
    * of the supplied function for each item in the original
    * array.
    */
    A.map = (Native.map) ?
        function(a, f, o) {
            return Native.map.call(a, f, o);
        } :
        function(a, f, o) {
            var results = [];
            A.each(a, function(item, i, a) {
                results.push(f.call(o, item, i, a));
            });
            return results;
        };

    /**
    * Executes the supplied function on each item in the array.
    * Reduce "folds" the array into a single value.
    * @method Array.reduce
    * @param a {Array} the array to iterate
    * @param init The initial value to start from
    * @param f {Function} the function to execute on each item. It
    * is responsible for returning the updated value of the
    * computation.
    * @param o Optional context object
    * @static
    * @return A value that results from iteratively applying the
    * supplied function to each element in the array.
    */
    A.reduce = (Native.reduce) ?
        function(a, init, f, o) {
            //Firefox's Array.reduce does not allow inclusion of a
            //  thisObject, so we need to implement it manually
            return Native.reduce.call(a, function(init, item, i, a) {
                return f.call(o, init, item, i, a);
            }, init);
        } :
        function(a, init, f, o) {
            var r = init;
            A.each(a, function (item, i, a) {
                r = f.call(o, r, item, i, a);
            });
            return r;
        };

    /**
    * Executes the supplied function on each item in the array,
    * searching for the first item that matches the supplied
    * function.
    * @method Array.find
    * @param a {Array} the array to search
    * @param f {Function} the function to execute on each item.
    * Iteration is stopped as soon as this function returns true
    * on an item.
    * @param o Optional context object
    * @static
    * @return {object} the first item that the supplied function
    * returns true for, or null if it never returns true
    */
    A.find = function(a, f, o) {
        var l = a.length;
        for(var i=0; i < l; i++) {
            if (f.call(o, a[i], i, a)) {
                return a[i];
            }
        }
        return null;
    };

    /**
    * Iterates over an array, returning a new array of all the elements
    * that match the supplied regular expression
    * @method Array.grep
    * @param a {Array} a collection to iterate over
    * @param pattern {RegExp} The regular expression to test against
    * each item
    * @static
    * @return {Array} All the items in the collection that
    * produce a match against the supplied regular expression.
    * If no items match, an empty array is returned.
    */
    A.grep = function (a, pattern) {
        return A.filter(a, function (item, index) {
            return pattern.test(item);
        });
    };

    /**
    * Partitions an array into two new arrays, one with the items
    * that match the supplied function, and one with the items that
    * do not.
    * @method Array.partition
    * @param a {Array} a collection to iterate over
    * @paran f {Function} a function that will receive each item
    * in the collection and its index.
    * @param o Optional execution context of f.
    * @static
    * @return An object with two members, 'matches' and 'rejects',
    * that are arrays containing the items that were selected or
    * rejected by the test function (or an empty array).
    */
    A.partition = function (a, f, o) {
        var results = {matches: [], rejects: []};
        A.each(a, function (item, index) {
            var set = f.call(o, item, index, a) ? results.matches : results.rejects;
            set.push(item);
        });
        return results;
    };

    /**
    * Creates an array of arrays by pairing the corresponding
    * elements of two arrays together into a new array.
    * @method Array.zip
    * @param a {Array} a collection to iterate over
    * @param a2 {Array} another collection whose members will be
    * paired with members of the first parameter
    * @static
    * @return An array of arrays formed by pairing each element
    * of the first collection with an item in the second collection
    * having the corresponding index.
    */
    A.zip = function (a, a2) {
        var results = [];
        A.each(a, function (item, index) {
            results.push([item, a2[index]]);
        });
        return results;
    };

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