How would I combine two arrays in Objective-C?

Question

What is the Objective-C equivalent of the JavaScript concat() function?

Assuming that both objects are arrays, how would you combine them?

It looks like you're doing calendrical operations. Please consider using NSCalendar and NSDateComponents and friends to do them for you. They are not a trivial subject. Are you taking leap months into account? How about daylight savings time? What about leap seconds? etc. — Dave DeLong
– Dave DeLong, Commented Jan 19, 2011 at 22:53
@DaveDeLong - Right now I'm porting a small Javascript Library. I will be refactoring code once I'm done with the actual rewrite. My first goal is to get the information in Objective-C and optimize later. — Moshe
– Moshe, Commented Jan 19, 2011 at 22:55

meaning-matters · Accepted Answer · 2017-06-10 12:05:24Z

221

NSArray's arrayByAddingObjectsFromArray: is more-or-less equivalent to JavaScript's .concat() method:

NSArray *newArray=[firstArray arrayByAddingObjectsFromArray:secondArray];

Note: If firstArray is nil, newArray will be nil. This can be fixed by using the following:

NSArray *newArray=firstArray?[firstArray arrayByAddingObjectsFromArray:secondArray]:[[NSArray alloc] initWithArray:secondArray];

If you want to strip-out duplicates:

NSArray *uniqueEntries = (NSArray *)[[NSSet setWithArray:newArray] allObjects];

edited Jun 10, 2017 at 12:05

meaning-matters

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answered Jan 19, 2011 at 22:46

grahamparks

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8 Comments

Moshe Over a year ago

Would this require an firstArray to be an NSMutableArray?

grahamparks Over a year ago

@Moshe It returns a new (immutable) NSArray object, and doesn't alter the original array, so it works fine on NSArray objects.

Ray Over a year ago

There is a potential problem with the answer, if the firstArray is nil but the second array is not, the newArray is nil.

Rickster Over a year ago

Sure, then add: if (!firstArray) firstArray = @[ ];

Andrew Bennett Over a year ago

then to make sure that you only get unique entries (if that's what you want): NSArray *uniqueEntries = [[NSSet setWithArray:newArray] allObjects];

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meaning-matters · Accepted Answer · 2017-06-10 12:15:44Z

10

Here's a symmetric & simple way by just beginning with an empty array:

NSArray* newArray = @[];
newArray = [newArray arrayByAddingObjectsFromArray:firstArray];
newArray = [newArray arrayByAddingObjectsFromArray:secondArray];

edited Jun 10, 2017 at 12:15

answered Jun 10, 2017 at 12:02

meaning-matters

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