CODEWITHSUNDEEP
objective-cnsarrayfast-enumeration
runmad
runmad

Reputation: 14886

Better solution for this 2x fast-enumeration?

I'm looping through an array and comparing the objects tag property in this array with the objects in another array.

Here's my code:

NSArray *objectsArray = ...;
NSArray *anotherObjectArray = ...;
NSMutableArray *mutableArray = ...;

for (ObjectA *objectA in objectsArray) {
    for (ObjectZ *objectZ in anotherObjectArray) {
        if ([objectA.tag isEqualToString:objectZ.tag]) {
            [mutableArray addObject:objectA];
        }
    }
}

Is there a better way to do this?

Please note the tag property is not an integer, so have to compare strings.

Upvotes: 1

Views: 166

Answers (4)

runmad
runmad

Reputation: 14886

Thanks for all the answers. While I have accepted the NSMutableSet solution, I actually ended up going with the following, as it turned out it was a tiny bit faster: 

NSMutableDictionary *tagDictionary = [NSMutableDictionary dictionaryWithCapacity:[anotherObjectArray count]];
for (ObjectZ *objectZ in anotherObjectArray) {
    [tagDictionary setObject:objectZ.tag forKey:objectZ.tag];
    }
for (ObjectA *objectA in objectsArray) {
    if ([tagDictionary objectForKey:objectA.tag]) {
        [direction addObject:objectA];
    }
}

Upvotes: 0

Seamus Campbell
Seamus Campbell

Reputation: 17906

You can do this by iterating over each array once, rather than nesting: 

NSMutableSet *tagSet = [NSMutableSet setWithCapacity:[anotherObjectArray count]];

for(ObjectZ *objectZ in antherObjectArray) {
    [tagSet addObject:objectZ.tag];
}

NSMutableArray *output = [NSMutableArray mutableArray];

for(ObjectA *objectA in objectsArray) {
    if([tagSet containsObject:objectA.tag]) {
        [output addObject:objectA];
    }
}

Upvotes: 5

mackworth
mackworth

Reputation: 5953

Well, the simplest change (as there can only be one match per objectA) then you could do a break after your [mutableArray addObject:objectA]. When a match occurs, that would reduce the inner loop by 50%.

More dramatically, if you're doing this a lot and the order of anotherObjectArray doesn't matter, would be to invert your anotherObjectArray data structure and use a dictionary, storing the objects by tag. Then you just iterate over objectA asking if its tag is in the dictionary of ObjectZs.

Upvotes: 1

Jirapong
Jirapong

Reputation: 24256

May be you can use [NSArray filteredArrayUsingPredicate:]; - http://developer.apple.com/library/mac/#documentation/Cocoa/Reference/Foundation/Classes/NSArray_Class/NSArray.html

But you may have to tweak for property tag yourself.

NSArray *objectsArray = [NSArray arrayWithObjects:@"Miguel", @"Ben", @"Adam", @"Melissa", nil];
NSArray *tagsArray = [NSArray arrayWithObjects:@"Miguel", @"Adam", nil];

NSPredicate *sPredicate = [NSPredicate predicateWithFormat:@"SELF IN %@", tagsArray];
NSArray *results = [objectsArray filteredArrayUsingPredicate:sPredicate];
NSLog(@"Matched %d", [results count]);
for (id a in results) {
    NSLog(@"Object is %@", a);
}

Hope this helps

Upvotes: 1

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