Get array of property value of each object in another array without a for loop

Question

This might be a basic question, but I can't seem to find an answer.

Suppose I have an NSArray (carArray) with objects of a certain type (Car).

Is it possible to get an NSArray (colorArray) with all values of a property (color) of these objects without iterating carArray with a for loop? (cfr. LINQ in .NET)

NSMutableArray *colorList = [[NSMutableArray alloc] initWithCapacity:0];

for (Car *car in carArray)
{
    [colorList addObject:car.color];
}

Thanks in advance.

Alladinian · Accepted Answer · 2012-03-27 13:31:58Z

83

Yes. Assuming that your object is adopting the KVC/KVO protocol. You can get an array of the properties like:

NSArray *colorList = [carArray valueForKey:@"color"];

Actually, what valueForKey: method does, is to return an array containing the results of invoking valueForKey: using key on each of the array's objects. (From Apple's Documentation on NSArray)

edited Mar 27, 2012 at 13:31

answered Mar 27, 2012 at 13:22

Alladinian

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2 Comments

Niels R. Over a year ago

I was looking at this method in the docs, but it wasn't very clear to me what is exactly did. I could just have tried it, of course.

damirstuhec Over a year ago

Beware that using wrong key will result in a crash at runtime. This approach has no type safety so you won't be warned by the compiler for using the wrong key.

Eduardo Viegas · Accepted Answer · 2015-07-10 23:12:02Z

16

Yes. You can do that without iterating it.

NSArray *colorArray = [carArray valueForKeyPath:@"@distinctUnionOfObjects.color"];

edited Jul 10, 2015 at 23:12

Eduardo Viegas

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answered Mar 27, 2012 at 13:24

Vignesh

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Comments

Code Lღver · Accepted Answer · 2012-03-28 06:31:33Z

-1

You can use the NSSet to get the colours:

NSSet *NScolors = [NSSet setWithArray:[carArray valueForKey:@"color"]];
NSArray *colors = [NScolors allObjects];

edited Mar 28, 2012 at 6:31

Code Lღver

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answered Mar 27, 2012 at 13:24

vadivelu

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