Creating an array from properties of objects in another array

Question

Is there any convenient way to take an array/set of objects and create a new array/set containing some property of each item in the first array?

For example, an array contains Car objects. I need an array of licensePlates, where each car has an NSObject car.licensePlate.

Currently I just iterate through the first array adding objects to my mutable results array, but was wondering if there is an instantiation method that exists for this (checked the docs for NSArray).

Mike Weller · Accepted Answer · 2012-03-27 13:56:03Z

119

This will return an array containing the value of licensePlate from each item in the myCars array:

NSArray *licensePlates = [myCars valueForKeyPath:@"licensePlate"]

If you want only unique items (for example), you can do something like this:

NSArray *licensePlates = [myCars valueForKeyPath:@"@distinctUnionOfObjects.licensePlate"];

For more possibilities, see the Collection Operators documentation in the Key-Value Coding Programming Guide.

edited Mar 27, 2012 at 13:56

answered Mar 27, 2012 at 13:50

Mike Weller

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2 Comments

Francesco Puglisi Over a year ago

I think the operator @unionOfObjects should be used in the first instance.

prad Over a year ago

Great answer! Looks like the link to docs is not working anymore. Here is the right link : developer.apple.com/library/content/documentation/Cocoa/…

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