Add sortBy method for interables

libraries/stdlib/src/kotlin/JLangIterablesSpecial.kt

@@ -71,6 +71,19 @@ public fun <T> java.lang.Iterable<T>.last() : T {
   return last;
 }
 
+/**
+ * Copies all elements into a [[List]] and sorts it by value of compare_function(element)
+ *
+ * E.g. arrayList("two" to 2, "one" to 1).sortBy({it._2}) returns list sorted by second element of tuple
+ *
+ * @includeFunctionBody ../../test/CollectionTest.kt sortBy
+ */
+public inline fun <in T, R: Comparable<in R>> java.lang.Iterable<T>.sortBy(f: (T) -> R): java.util.List<T> {
+    val sortedList = this.toList()
+    java.util.Collections.sort(sortedList, comparator {(x, y) -> f(x).compareTo(f(y))})
+    return sortedList
+}
+
 /**
  * Checks if collection contains given item.
  *