DasGenie: !Scrap: Iterating over an NSIndexSet

Samstag, 8. Januar 2005

Iterating over an NSIndexSet

Since I needed this quite a lot and the original Apple documentation isn't very helpful here, I decided to post my 2 favorite ways of iterating over an NSIndexSet:

// easy and still reasonable fast - can be reversed by using lastIndex and indexLessThanIndex:

unsigned index = [indexSet firstIndex];

while (index!=NSNotFound) {

    // do Stuff

    index=[indexSet indexGreaterThanIndex:index]) {

}

This seems a little bit inefficient, but I was made belief (by mmalc) that indexGreaterThanIndex: behaves efficient when called this way.

Nevertheless if you want full speed at possibly large sets, then go for this one:

// more complex but as efficient as you choose your buffersize

unsigned int indexBuffer[40];

unsigned int bufferIndex;

unsigned int indexCount=1;

NSRange range=NSMakeRange([indexSet firstIndex],

                          [indexSet lastIndex]-[indexSet firstIndex]+1);

while ((indexCount=[indexSet getIndexes:indexBuffer maxCount:40 inIndexRange:&range])) {

    for (bufferIndex=0;bufferIndex<indexCount;bufferIndex++) {

        unsigned int index=indexBuffer[bufferIndex];

        // do stuff

    }

}

If you know a way to reverse the direction of this one please add a comment.

20:26 - Samstag, 8. Januar 2005

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