arrays - Two NSArrays combine to a NSDictionary with alternating values

Question

Hi I am very new to Objective-c please excuse my ignorance. So basically this is what I want to happened. I have two arrays of numbers

Array1: (1,3,5);
Array2: (2,4,6);

and I want them to be like this after combining them in a dictionary

"dictionary":{"1":2,: "3":4, "5":6}

Any feedback will be appreciated!

Answer 1

Arrays

I have two arrays of numbers Array1: (1,3,5) & Array2: (2,4,6)

I assume that you have them in NSArray and that you're aware of NSNumber & Objective-C Literals. In other words, you have:

NSArray *keys    = @[@1, @3, @5]; // Array of NSNumber
NSArray *objects = @[@2, @4, @6]; // Array of NSNumber

"dictionary":{"1":2,: "3":4, "5":6}

I assume that it means:

@{
    @"dictionary": @{
        @"1": @2,
        @"3": @4,
        @"5": @6
    }
}

Step 1 - Stringify keys

NSArray *keys = @[@1, @3, @5];
NSArray *objects = @[@2, @4, @6];

NSMutableArray *stringifiedKeys = [NSMutableArray arrayWithCapacity:keys.count];
for (NSNumber *key in keys) {
    [stringifiedKeys addObject:key.stringValue];
}

Step 2 - Create a dictionary

dictionaryWithObjects:forKeys::

+ (instancetype)dictionaryWithObjects:(NSArray<ObjectType> *)objects 
                              forKeys:(NSArray<id<NSCopying>> *)keys;

You can use it in this way:

NSArray *keys = @[@1, @3, @5];
NSArray *objects = @[@2, @4, @6];

NSMutableArray *stringifiedKeys = [NSMutableArray arrayWithCapacity:keys.count];
for (NSNumber *key in keys) {
    [stringifiedKeys addObject:key.stringValue];
}

NSDictionary *dictionary = [NSDictionary dictionaryWithObjects:objects
                                                       forKeys:stringifiedKeys];

Step 3 - Wrap it in a dictionary

NSArray *keys = @[@1, @3, @5];
NSArray *objects = @[@2, @4, @6];

NSMutableArray *stringifiedKeys = [NSMutableArray arrayWithCapacity:keys.count];
for (NSNumber *key in keys) {
    [stringifiedKeys addObject:key.stringValue];
}

NSDictionary *dictionary = [NSDictionary dictionaryWithObjects:objects
                                                       forKeys:stringifiedKeys];
NSDictionary *result = @{ @"dictionary": dictionary };

NSLog(@"%@", result);

Result:

{
    dictionary = {
        1 = 2;
        3 = 4;
        5 = 6;
    };
}

Manually

NSArray *keys = @[@1, @3, @5];
NSArray *objects = @[@2, @4, @6];

// Mimick dictionaryWithObjects:forKeys: behavior
if (objects.count != keys.count) {
    NSString *reason = [NSString stringWithFormat:@"count of objects (%lu) differs from count of keys (%lu)", (unsigned long)objects.count, (unsigned long)keys.count];

    @throw [NSException exceptionWithName:NSInvalidArgumentException
                                   reason:reason
                                 userInfo:nil];
}

NSMutableDictionary *inner = [NSMutableDictionary dictionaryWithCapacity:keys.count];

for (NSUInteger index = 0 ; index < keys.count ; index++) {
    NSString *key = [keys[index] stringValue];
    NSString *object = objects[index];
    inner[key] = object;
}

NSDictionary *result = @{ @"dictionary": inner };

Footnotes

Because of I am very new to Objective-C, I did intentionally avoid:

• Blocks & safer ways to enumerate
• Lightweight generics
• Nullability stuff