List<DataSetIntervalIndex> intervalsIdxs = lastGroupIndex.getIntervalIndexes();
for (DataSetIntervalIndex intervalIndex : intervalsIdxs) {
// In a nested group the intervals can aggregate other intervals.
if (intervalIndex instanceof DataSetIntervalSetIndex) {
DataSetIntervalSetIndex indexSet = (DataSetIntervalSetIndex) intervalIndex;
for (DataSetIntervalIndex subIndex : indexSet.getIntervalIndexes()) {
nestedContext.index = subIndex;
DataSetGroupIndex sg = singleGroup(op, nestedContext);
nestedGroupIndex.indexIntervals(sg.getIntervalIndexes());
}
}