Question

How may I find a certain string (value) in an NSSet?
Must this be done using predicates? If so, how?

NSMutableSet *set = [[NSMutableSet alloc] init];
[set addObject:[[[NSString alloc] initWithFormat:@"String %d", 1] autorelease]];
[set addObject:[[[NSString alloc] initWithFormat:@"String %d", 2] autorelease]];
[set addObject:[[[NSString alloc] initWithFormat:@"String %d", 3] autorelease]];

Now I want to check if ‘String 2’ exists in the set.

Answer 1

From Apple’s Developer Site:

NSSet *sourceSet = [NSSet setWithObjects:@"One", @"Two", @"Three", @"Four", nil];
NSPredicate *predicate = [NSPredicate predicateWithFormat:@"SELF beginswith 'T'"];
NSSet *filteredSet = [sourceSet filteredSetUsingPredicate:predicate];
// filteredSet contains (Two, Three)

This article from Ars Technica contains some more information on using predicates. Finally Apple’s BNF guide for predicates contains information on all operations one might need.