/**
* Partitions the instances around a pivot. Used by quicksort and kthSmallestValue.
*
* @param insts The instances on which the tree is (or is to be) built.
* @param index The master index array containing indices of the instances.
* @param attidx The attribution/dimension based on which the instances should be partitioned.
* @param l The begining index of the portion of master index array that should be partitioned.
* @param r The end index of the portion of master index array that should be partitioned.
* @return the index of the middle element
*/
protected static int partition(Instances insts, int[] index, int attidx, int l, int r) {
double pivot = insts.instance(index[(l + r) / 2]).value(attidx);
int help;
while (l < r) {
while ((insts.instance(index[l]).value(attidx) < pivot) && (l < r)) {
l++;
}
while ((insts.instance(index[r]).value(attidx) > pivot) && (l < r)) {
r--;
}
if (l < r) {
help = index[l];
index[l] = index[r];
index[r] = help;
l++;
r--;
}
}
if ((l == r) && (insts.instance(index[r]).value(attidx) > pivot)) {
r--;
}
return r;
}
/**
* Method to validate the sorting done by quickSort().
*
* @param insts The instances on which the tree is (or is to be) built.
* @param indices The master index array containing indices of the instances.
* @param attidx The dimension/attribute based on which the instances should be sorted.
* @param start The start of the portion in master index array that needs to be sorted.
* @param end The end of the portion in master index array that needs to be sorted.
* @throws Exception If the indices of the instances are not in sorted order.
*/
private static void checkSort(Instances insts, int[] indices, int attidx, int start, int end)
throws Exception {
for (int i = start + 1; i <= end; i++) {
if (insts.instance(indices[i - 1]).value(attidx) > insts.instance(indices[i]).value(attidx)) {
System.out.println("value[i-1]: " + insts.instance(indices[i - 1]).value(attidx));
System.out.println("value[i]: " + insts.instance(indices[i]).value(attidx));
System.out.println("indices[i-1]: " + indices[i - 1]);
System.out.println("indices[i]: " + indices[i]);
System.out.println("i: " + i);
if (insts.instance(indices[i - 1]).value(attidx) > insts.instance(indices[i]).value(attidx))
System.out.println("value[i-1] > value[i]");
throw new Exception("Indices not sorted correctly.");
} // end if
}
}