Merge pull request #135 from karypid/karypid

Add unordered remove to primitive collection

agrona/src/main/java/org/agrona/collections/IntArrayList.java

@@ -319,6 +319,36 @@ public Integer remove(
         return value;
     }
 
+    /**
+     * Removes element at index, but instead of copying all elements to the
+     * left, moves into the same slot the last element. This avoids the copy
+     * costs, but spoils the list order. If index is the last element it is just
+     * removed.
+     *
+     * @param index
+     *            of the element to be removed.
+     * @return the existing value at this index.
+     * @throws IndexOutOfBoundsException
+     *             if index is out of bounds.
+     */
+    public int fastUnorderedRemove(
+        @DoNotSub final int index)
+    {
+        checkIndex(index);
+
+        final int value = elements[index];
+
+        @DoNotSub final int moveCount = size - index - 1;
+        if (moveCount > 0)
+        {
+            elements[index] = elements[size - 1];
+        }
+
+        size--;
+
+        return value;
+    }
+
     /**
      * Remove the first instance of a value if found in the list.
      *

agrona/src/test/java/org/agrona/collections/IntArrayListTest.java

@@ -138,6 +138,18 @@ public void shouldRemoveAtIndex()
         assertThat(list.getInt(10), is(11));
     }
 
+    @Test
+    public void shouldFastRemoveUnorderedAtIndex()
+    {
+        final int count = 20;
+        IntStream.range(0, count).forEachOrdered(list::addInt);
+
+        assertThat(list.fastUnorderedRemove(10), is(10));
+
+        assertThat(list.size(), is(count - 1));
+        assertThat(list.getInt(10), is(19));
+    }
+
     @Test
     public void shouldForEachOrderedInt()
     {