How do I put objects in an NSArray into an NSSet?

Question

Hi all, I have some NSDictionary objects stored in an NSArray called telephoneArray. I fetch the values for the key number and then replace the NSDictionary I've just read with a new object at the same index in the array. I then want to put these new objects into an NSSet. How can this be achieved? See my unsuccessful attempt below.

    // Add all telephones to this branch
    for (int i=0; i<[telephoneArray count]; i++) {

        [newTelephone setBranch:newBranch];
        [newTelephone setNumber:[[telephoneArray objectAtIndex:i] valueForKey:@"number"]];

        NSLog(@"%@",[[telephoneArray objectAtIndex:i] valueForKey:@"number"]);
        [telephoneArray replaceObjectAtIndex:i withObject:newTelephone];
        NSLog(@"phone number %i = %@",i,[[telephoneArray objectAtIndex:i] valueForKey:@"number"]);

    }

    NSSet *telephoneSet = [NSSet setWithArray:telephoneArray];

    NSLog(@"telephoneArray=%i",[telephoneArray count]);
    NSLog(@"telephoneSet=%i",[[telephoneSet allObjects] count]);

OUTPUT:

2010-03-06 03:06:02.824 AIB[5160:6507] 063 81207
2010-03-06 03:06:02.824 AIB[5160:6507] phone number 0 = 063 81207
2010-03-06 03:06:02.825 AIB[5160:6507] 063 81624
2010-03-06 03:06:02.825 AIB[5160:6507] phone number 1 = 063 81624
2010-03-06 03:06:02.825 AIB[5160:6507] 063 81714
2010-03-06 03:06:02.826 AIB[5160:6507] phone number 2 = 063 81714
2010-03-06 03:06:02.826 AIB[5160:6507] 063 81715
2010-03-06 03:06:02.826 AIB[5160:6507] phone number 3 = 063 81715
2010-03-06 03:06:02.826 AIB[5160:6507] telephoneArray=4
2010-03-06 03:06:02.827 AIB[5160:6507] telephoneSet=1

With the code above, telephoneArray can have a count of between 1 and 5 but telephoneSet always has a value of 1. I assume there's an obvious mistake but I can't see where.

Answer 1

This is not correct:

NSSet *telephoneSet = [[NSSet alloc] init];
[telephoneSet setByAddingObjectsFromArray:telephoneArray];

That method returns an NSSet which you are doing nothing with (it doesn't add the objects to telephoneSet, it creates a new NSSet). Do this instead:

NSSet *telephoneSet = [NSSet setWithArray:telephoneArray]

Also, note that a set cannot contain duplicates unlike an array. So if you have duplicate objects in your array and you put them in a set, the duplicates will be removed which can affect the object count.

Answer 2

Initially telephoneArray contains references to n distinct objects. After the loop ends, it does contain n references, but each one is pointing to the same newTelephone object.

Array can contain duplicates, so it doesn't matter. A Set cannot have duplicates, and your entire telephoneArray is composed of a single object basically, so you're seeing just one.

In your loop, you have to create a new object or get a telephone object from somewhere:

for (int i=0; i<[telephoneArray count]; i++) {
    // Create the new object first, or get it from somewhere.
    Telephone *newTelephone = [[Telephone alloc] init];
    [newTelephone setBranch:newBranch];
    [newTelephone setNumber:[[telephoneArray objectAtIndex:i] valueForKey:@"number"]];
    [telephoneArray replaceObjectAtIndex:i withObject:newTelephone];
    // the array holds a reference, so you could let go of newTelephone
    [newTelephone release];
}

Also, like PCWiz said, you don't need to allocate a new NSSet object in your case. Just call the class method setWithArray:.

NSSet *telephoneSet = [NSSet setWithArray:telephoneArray]