Question

I’m tried to get column array like following without NSDictionary.
it works well.

But I’d like to know if objective-c literal supports this feature.

Is there a literal to do like this?

e.g array[][0]?, array[*][0], array[?][0], etc..?

NSArray *array1 = @[@"AAa", @"BBB", @"CCC"];
NSArray *array2 = @[@"AAb", @"BBB", @"CCC"];
NSArray *array3 = @[@"AAc", @"BBB", @"CCC"];

array = @[array1, array2, array3];

NSArray *result;
result = [self getColumnArray:0]; // <- get array's [*][0]
NSLog(@"result is : %@", result);

result = [self getColumnArray:2]; // <- get array's [*][2]
NSLog(@"result is : %@", result);


- (NSArray *)getColumnArray:(NSUInteger)index {
    NSMutableArray *resultArray = [NSMutableArray array];

    for (NSArray *item in array) {
        [resultArray addObject:item[index]];
    }

    return resultArray;
}


Excuted result :

2012-10-29 16:00:24.550 testButton[28245:11303] result is : (
    AAa,
    AAb,
    AAc
)
2012-10-29 16:00:24.552 testButton[28245:11303] result is : (
    CCC,
    CCC,
    CCC
)

Answer 1

The following code will work:

NSArray *arr = @[ @[@"A", @"B"], @[@"C", @"D"]];
NSLog(@"%@", array[0][0]); // Logs 'A'

Therefore you could do something like this to achieve your desired effect:

// Log the 0 element of each NSArray within your primary array.
NSArray *primaryArray = @[ @[@"A", @"1"], @[@"A", @"2"], @[@"A", @"3"] ];
for (int i = 0; i < array.count; i++) {

     NSLog(@"%@", primaryArray[i][0]); // Logs "AAA"

}
// Or you can use a for (NSArray *arr in primaryArray) fast-enumeration loop.

As far as I’m aware though, there is no syntax for:

NSLog(@"%@", primaryArray[*][0]); // Could log "AAA"

There are several reasons for this.

1. There is no specification of how long primaryArray is.
2. NSLog has no idea how many %@‘s it needs (similar reasons for other uses, e.g. how would you return primaryArray[*][0]?)
3. You are condensing an O(n) process into a single call. This could be forgiven if there was documented API for it.
4. For this to be possible, the * operator would have to be overloaded (in this case to a ‘wildcard’ function) and Objective-C does not support operator overloading (except when done inside the compiler, which I suppose is no longer ‘operator overloading’ but ‘adding a language feature’). Also, * already denotes a pointer in C and ? is used in the ?: ternary operator.
5. Objective-C already has a fast-enumeration structure which handles these situations, if this syntax were to be added, you’d be reinventing the wheel a little.

In short, a fast-enumeration loop is the best way to do what you want, and the nested [i][0] box syntax aids its readability slightly. I agree the wildcard syntax would be very handy in some cases (such as logging and enumeration), but I think it would be too difficult to implement succinctly across the board. Plus, since they overloaded ^ for blocks, they’re running out of usable operators!