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?

score 40 · Accepted Answer · answered Apr 21 '10 at 05:05

40

Yes, use the NSArray -valueForKey: method.

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

answered Apr 21 '10 at 05:05

David Gelhar

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@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! :) – Itai Spector Sep 15 '16 at 07:35
Can we do this for a set of keys, or is it available for only one key? – nr5 Jul 29 '17 at 18:57
This kind of method available in `Swift`? – Mathi Arasan Aug 09 '17 at 12:24
@user3589771 check out this question https://stackoverflow.com/questions/26367261/key-value-coding-kvc-with-array-dictionary-in-swift for some possible solutions in Swift – David Gelhar Aug 09 '17 at 15:18
Thanks, I saw that, [Accepted answer](https://stackoverflow.com/a/26367532/3589771) not works for me. Finally, I used [this answer](https://stackoverflow.com/a/30693198/3589771). I tried if swift provide single line like obj-c. – Mathi Arasan Aug 10 '17 at 11:39

score 12 · Answer 2 · answered Apr 21 '10 at 05:06

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);

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

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