Caleb Madrigal

Programming, Hacking, Math, and Art

  

Map in Objective-C

Today, I was faced with an issue several times where I had an array of items of one type, and had to convert this into an array of items of a different type. This made me really want a map() function. So I added one to NSArray like so:

NSArray+FP.h

#import <Foundation/Foundation.h>
typedef id(^MapBlock)(id);
@interface NSArray (FP)
- (NSArray *)map:(MapBlock)block;
@end

NSArray+FP.m

#import "NSArray+FP.h"
@implementation NSArray (FP)
- (NSArray *)map:(MapBlock)block {
    NSMutableArray *resultArray = [[NSMutableArray alloc] init];
    for (id object in self) {
        [resultArray addObject:block(object)];
    }
    return resultArray;
}
@end

So now, I can do this!

NSArray *strArray = [NSArray arrayWithObjects:@"1",@"1",@"2",@"3",@"5",@"8",nil];
NSArray *numArray = [strArray map:^id(id object) {
    NSString *str = object;
    return [NSNumber numberWithInt:[str intValue]];
}];

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