Compare two NSArrays and return number of differences

Question

How can I take two NSArrays, compare them, then return the number of differences, preferably the number of different objects, for example:

Array 1: one two

Answer 1

I found that the answer above didn't take arrays of differing size into account. If you do it as above, you should check to see which array.count is smaller and

[largerArray removeObjectsInArray:shorterArray];

OR

I made them both NSSets and then compared.

[set1 isEqualToSet:set2];

That way size and order are both dealt with properly! (I didn't need to know the number of differences)

Answer 2

You can do this by using an intermediate NSMutableArray:

NSArray *array1 = [NSArray arrayWithObjects:@"One", @"Two", @"Three", nil];
NSArray *array2 = [NSArray arrayWithObjects:@"Two", @"Four", @"One", nil];
NSMutableArray *intermediate = [NSMutableArray arrayWithArray:array1];
[intermediate removeObjectsInArray:array2];
NSUInteger difference = [intermediate count];

With that way, only common elements will be removed.