Creating an array from properties of objects in another array

objective-c nsarray nsset
Ben Packard picture Ben Packard · Mar 27, 2012 · Viewed 12.9k times · Source

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).

Answer

Mike Weller picture Mike Weller · Mar 27, 2012

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.

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