Question

I did some runs on my iOS app with Instruments and I saw that 90% of the load on the main thread on launch (about 1000ms total) is caused by containsObject: calls. That’s on the main thread and I don’t think it’s cool.

Is there a faster alternative to this method? An algorithm or another method?

Any suggestions?

MORE INFO:

1. I looked into my code again I realized that in fact I don’t need to know the order of the objects, only if an object is part of that set. Which means NSSet will do just fine (and I guess is faster).

2. Number of objects – there may very well be 1000+ objects in that set.

Answer 1

If you NEED to use an array, skip a bit further down

---

Alternate Options

Your other options might include:

• Using an NSDictionary which uses key->value pairs which (I expect will) have O(1) read complexity at the cost of extra storage space for the keys

• If you aren’t using duplicates and order isn’t important, using an NSSet will offer better read complexity (I don’t know what the complexity will be, the docs probably will)

---

Using an Array

If you keep the array sorted, searching can be done in O(log n) time instead of O(n) as you can take advantage of a binary search.

Caveat Lector: This was written from memory

-(void) /*adding*/
{
    int proposedIndex = 0;
    proposedIndex = [array indexOfObject:node
                                inSortedRange:NSMakeRange(0, array.count)
                                      options:NSBinarySearchingInsertionIndex
                              usingComparator:
                      ^ NSComparisonResult(id obj1, id obj2)
                      {
                          if (obj1.valueToCompare < obj2.valueToCompare) return NSOrderedAscending;
                          if (obj1.valueToCompare > obj2.valueToCompare) return NSOrderedDescending;
                          else return NSOrderedSame;
                      }];

    [array insertObject:node atIndex:proposedIndex];
}


-(id) /* Getting */
{
    int location = [array indexOfObject:node
                                    inSortedRange:NSMakeRange(0, array.count)
                                          options:NSBinarySearchingFirstEqual
                                  usingComparator:
                          ^ NSComparisonResult(id obj1, id obj2)
                          {
                              if (obj1.valueToCompare < obj2.valueToCompare) return NSOrderedAscending;
                              if (obj1.valueToCompare > obj2.valueToCompare) return NSOrderedDescending;
                              else return NSOrderedSame;
                          }];
    if (location == NSNotFound) return nil;
    return [array objectAtIndex:location];
}