--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/edu/unc/utils/SortUtils.java	Mon Feb 13 22:12:06 2012 -0500
@@ -0,0 +1,60 @@
+package edu.unc.utils;
+
+/**
+ * Custom sorting utilities
+ * see: http://stackoverflow.com/questions/951848/java-array-sort-quick-way-to-get-a-sorted-list-of-indices-of-an-array
+ * @author timpalpant
+ *
+ */
+public class SortUtils {
+	public static int[] indexSort(float[] main) {
+		int[] index = new int[main.length];
+		for (int i = 0; i < index.length; i++) {
+			index[i] = i;
+		}
+		
+		quicksort(main, index, 0, index.length-1);
+		
+		return index;
+	}
+
+	// quicksort a[left] to a[right]
+	public static void quicksort(float[] a, int[] index, int left, int right) {
+		if (right <= left)
+			return;
+		int i = partition(a, index, left, right);
+		quicksort(a, index, left, i - 1);
+		quicksort(a, index, i + 1, right);
+	}
+
+	// partition a[left] to a[right], assumes left < right
+	private static int partition(float[] a, int[] index, int left, int right) {
+		int i = left - 1;
+		int j = right;
+		while (true) {
+			while (a[index[++i]] < a[index[right]])
+				// find item on left to swap
+				; // a[right] acts as sentinel
+			while (a[index[right]] < a[index[--j]])
+				// find item on right to swap
+				if (j == left)
+					break; // don't go out-of-bounds
+			if (i >= j)
+				break; // check if pointers cross
+			exch(a, index, i, j); // swap two elements into place
+		}
+		exch(a, index, i, right); // swap with partition element
+		return i;
+	}
+
+	// exchange a[i] and a[j]
+	private static void exch(float[] a, int[] index, int i, int j) {
+		// Don't swap the data
+		// float swap = a[i];
+		// a[i] = a[j];
+		// a[j] = swap;
+		int b = index[i];
+		index[i] = index[j];
+		index[j] = b;
+	}
+}