Comparing Two Arrays.

Question

I have two NSArrays, what I'm looking to do is to compare two arrays which contain strings, find the similarities and create the first array again but so they have no similarities.

Just for an example something like.

Two Arrays:

NSArray *arrayOne = [NSArray arrayWithObjects:@"TD1", @"TD2", @"TD3", nil];
NSArray *arrayTwo = [NSArray arrayWithObjects:@"Blah", @"String", @"TD2", nil];

Outcome:

NSArray *arrayOne = [NSArray arrayWithObjects:@"TD1", @"TD2", @"TD3", nil];

NSArray *arrayOneCopy = [NSArray arrayWithObjects:@"TD1", @"TD3", nil];
NSArray *arrayTwo = [NSArray arrayWithObjects:@"Blah", @"String", @"TD2", nil];

Answer 1

NSMutableArray *arrayOneCopy = [NSMutableArray arrayWithArray:arrayOne];
[arrayOneCopy removeObjectsInArray:arrayTwo];

Answer 2

Use NSSet.

NSSet *setOne = [NSMutableSet setWithArray: arrayOne];
NSSet *setTwo = [NSSet setWithArray: arrayTwo];

[setOne minusSet: setTwo];

NSArray *arrayOneResult = [setOne allObjects];

Or use NSArray as the other person answered -- that works, too.

Which one works depends entirely on your data set size. For small sets of data, the array solution works fine. For larger sets, NSSet will be much more efficient in that membership tests are a hash check and not a linear search.

Measure and use the one that works best.