Ole Begemann on binary searching an NSArray:
…NSArray comes with a binary search method named indexOfObject:inSortedRange:options:usingComparator:. Using this method can greatly speed up searching but requires the array to be sorted.
And “greatly speed up” translates to:
Searching a sorted array of 100,000 elements using binary search would require at most 17 comparisons compared to the 50,000 comparisons a naive linear search would take on average.