Manipulating Indexes

From: indexset.m

13 NSMutableIndexSet *indexSet =
14   [NSMutableIndexSet indexSetWithIndex: 1];
15 [indexSet addIndexesInRange:
16   NSMakeRange(5, 20)];
17 [array removeObjectsAtIndexes:
18   indexSet];

Arrays are indexed by integers. Often, you want to do some operation on a group of values in an array. A special class, called NSIndexSet, is used for storing groups of indexes. Internally, this stores a set of ranges, so can be quite dense.