Add orderBy filter.

Author: addyosmani

filter-orderBy.js

@@ -0,0 +1,70 @@
+PolymerExpressions.prototype.orderBy = function (array, columnsToOrderBy, reverse) {
+    if (!Array.isArray(array)) {
+        return array;
+    }
+    if (!columnsToOrderBy) {
+        return array;
+    }
+    if (typeof columnsToOrderBy === 'string') {
+        columnsToOrderBy = [columnsToOrderBy];
+    }
+
+    // on a column-by-column basis, determine if descending order is desired
+    var reverseSortValues = [];
+    columnsToOrderBy.forEach(function (element, index) {
+        if (element[0] == '-') {
+            columnsToOrderBy[index] = element.substr(1);
+            reverseSortValues.push(true);
+        } else {
+            reverseSortValues.push(false);
+        }
+    });
+
+    // temporary holder of position and sort-values
+    var map = array.map(function (element, index) {
+        var sortValues = columnsToOrderBy.map(function (key) {
+            if (typeof element[key] === 'string') {
+                return element[key].toLowerCase();
+            }
+
+            return element[key];
+        });
+
+        return {
+            index: index,
+            sortValues: sortValues
+        };
+    });
+
+    // sorting the map containing the reduced values
+    map.sort(function (a, b) {
+        var length = a.sortValues.length;
+
+        for (var i = 0; i < length; i++) {
+            if (reverseSortValues[i] === false) {
+                if (a.sortValues[i] < b.sortValues[i])
+                    return -1;
+                else if (a.sortValues[i] > b.sortValues[i])
+                    return 1;
+            } else {
+                if (a.sortValues[i] > b.sortValues[i])
+                    return -1;
+                else if (a.sortValues[i] < b.sortValues[i])
+                    return 1;
+            }
+        }
+
+        return 0;
+    });
+
+    if (reverse === true) {
+        map.reverse();
+    }
+
+    // container for the resulting order
+    var result = map.map(function (element) {
+        return array[element.index];
+    });
+
+    return result;
+};