it would be the proper way:
NSIndexSet *indexSet = [NSIndexSet indexSetWithIndexesInRange:NSMakeRange(0, 3)];
or you can use the NSMutableIndexSet
for the random indexes:
NSMutableIndexSet *mutableIndexSet = [[NSMutableIndexSet alloc] init];
[mutableIndexSet addIndex:0];
[mutableIndexSet addIndex:2];
[mutableIndexSet addIndex:9];
etc.