Question

I have an array, which contains some duplicate entries.

Firstly, is there any way to restrict duplicate entries when data getting inserted?

Secondly, if an array already having duplicate values than in some other way, we can retrieve only unique values from that array, I heard about NSSet about this, but I have no idea how to use it.

Answer 1

Don’t use an NSSet.

You can only insert elements upon creation and cannot change the elements contained after you have created it.

If you want to add and remove objects on the fly, you can use an NSMutableSet.

Here is a demo of how to use it both NSSet and NSMutableSet, then converting the NSSet back to an NSArray (incase you want to do that):

- (void) NSMutableSetPrintTest
{
    NSMutableSet *mutableSet = [[NSMutableSet alloc] init];

    NSLog(@"Adding 5 objects (3 are duplicates) to NSMutableSet");
    NSString *firstString = @"Hello World";
    [mutableSet addObject:firstString];
    [mutableSet addObject:@"Hello World"];
    [mutableSet addObject:@"Goodbye World"];
    [mutableSet addObject:@"Goodbye World"];
    [mutableSet addObject:@"Goodbye World"];

    NSLog(@"NSMutableSet now contains %d objects:", [mutableSet count]);
    int j = 0;
    for (NSString *string in mutableSet) {
        NSLog(@"%d: %@ <%p>", j, string, string);
        j++;
    }

    NSLog(@"Now, if we are done adding and removing things (and only want to check what is in the Set) we should convert to an NSSet for increased performance.");
    NSSet *immutableSet = [NSSet setWithSet:mutableSet];

    NSLog(@"NSSet now contains %d objects:", [immutableSet count]);
    int i = 0;
    for (NSString *string in immutableSet) {
        NSLog(@"%d: %@ <%p>", i, string, string);
        i++;
    }

    [mutableSet release]; mutableSet = nil;

    NSLog(@"Now, if we are done with the sets, we can convert them back to an NSArray:");
    NSArray *array = [immutableSet allObjects];

    NSLog(@"NSArray contains %d objects", [array count]);
    int k = 0;
    for (NSString *string in array) {
        NSLog(@"%d: %@ <%p>", k, string, string);
        k++;
    }
}