Question

I have a NSArray of string id and a NSDictionary of NSDictionary objects. I am currently looping through the string id array to match the id value in the NSDictionary.

There are around 200 NSDictionary objects and only 5 or so string ID.

My current code is such:

for (NSString *Str in aArr) {
        for (NSDictionary *a in apArr)
        {
            if ([a objectForKey:@"id"] == Str)
            {
            NSLog(@"Found!");
            }
        }
}

The performance of the above code is really slow and I was wondering if there is a better way to do this?

Answer 1

I’d implement your code in the following way:

for (NSDictionary *a in apArr)
{
    if ([aArr containsObject:[a objectForKey:@"id"]])
    {
        NSLog(@"Found!");
    }
}

I’m still not sure about containsObject performance, but, I guess there should be SDK optimizations to find objects faster than O(n).

Added:

Another suggestion. I suppose, that “id” field is unique for all NSDictionary objects. If it is so, you can remap your NSArray of NSDictionaries to NSDictionary:

from:

index -> NSDictionary

to:

id -> NSDictionary

And you will find elements for O(1) instead of O(n).

Re remapping. Either you should create NSDictionary with appropriate format (id -> object) or you may remap your array in the following way:

NSMutableDictionary *md = [[NSMutableDictionary alloc] init];
for ( NSDicationary *a in apArr ) {
    [md setObject:a forKey:[a objectForKey:@"id"]];
}