lajos lajos - 3 months ago 18
Objective-C Question

filtering NSArray into a new NSArray in objective-c

I have an

NSArray
and I'd like to create a new
NSArray
with objects from the original array that meet certain criteria. The criteria is decided by a function that returns a
BOOL
.

I can create an
NSMutableArray
, iterate through the source array and copy over the objects that the filter function accepts and then create an immutable version of it.

Is there a better way?

Answer

NSArray and NSMutableArray provide methods to filter array contents. NSArray provides filteredArrayUsingPredicate: which returns a new array containing objects in the receiver that match the specified predicate. NSMutableArray adds filterUsingPredicate: which evaluates the receiver’s content against the specified predicate and leaves only objects that match. These methods are illustrated in the following example.

NSMutableArray *array =
    [NSMutableArray arrayWithObjects:@"Bill", @"Ben", @"Chris", @"Melissa", nil];

NSPredicate *bPredicate =
    [NSPredicate predicateWithFormat:@"SELF beginswith[c] 'b'"];
NSArray *beginWithB =
    [array filteredArrayUsingPredicate:bPredicate];
// beginWithB contains { @"Bill", @"Ben" }.

NSPredicate *sPredicate =
    [NSPredicate predicateWithFormat:@"SELF contains[c] 's'"];
[array filterUsingPredicate:sPredicate];
// array now contains { @"Chris", @"Melissa" }