From array of dictionaries, make array containing values of one key

Question

I have an array of dictionaries. I would like to extract an array with all the elements of one particular key of the dictionaries in the original array. Can this be done without enumeration?

Solution 1

Yes, use the NSArray -valueForKey: method.

NSArray *extracted = [sourceArray valueForKey:@"a key"];

Solution 2

Yes, just use Key-Value Coding to ask for the values of the key:

NSArray* names = [NSArray arrayWithObjects:
                  [NSDictionary dictionaryWithObjectsAndKeys:
                   @"Joe",@"firstname",
                   @"Bloggs",@"surname",
                   nil],
                  [NSDictionary dictionaryWithObjectsAndKeys:
                   @"Simon",@"firstname",
                   @"Templar",@"surname",
                   nil],
                  [NSDictionary dictionaryWithObjectsAndKeys:
                   @"Amelia",@"firstname",
                   @"Pond",@"surname",
                   nil],
                  nil];

//use KVC to get the names
NSArray* firstNames = [names valueForKey:@"firstname"];

NSLog(@"first names: %@",firstNames);

Comments

[Itai Spector]

@e.James, you learn if you ask and your curious. I came up with the thought about how to implement this, because i didn't want to loop around and do like the old-school style. I'm glad I looked for a way of doing that, and like you say, learnt another new thing, cheers for learning everyday! :)

[nr5]

Can we do this for a set of keys, or is it available for only one key?

[Mathi Arasan]

This kind of method available in Swift?

[David Gelhar]

@user3589771 check out this question stackoverflow.com/questions/26367261/… for some possible solutions in Swift

[Mathi Arasan]

Thanks, I saw that, Accepted answer not works for me. Finally, I used this answer. I tried if swift provide single line like obj-c.