A category on NSDictionary that remaps the keys to new keys provided in the mapping, optionally removing null values.

NSDictionary+JCSKeyMapping.h

//
//  NSDictionary+JCSKeyMapping.h
//
//  Created by Abizer Nasir on 06/08/2013.
//

#import <Foundation/Foundation.h>

@interface NSDictionary (JCSKeyMapping)

/*! A category method that replaces the keys in the receiver with the new key provided in the keyMapping
 *
 *  If no mapping is provided for a key, the key is left unchanged.
 *  \param keymapping a dictionary which maps the existing key to the new key. If no mapping is provided for a key it is unchanged.
 *  \param removeNulls If YES, then if the value for a key in the receiver is [NSNull null], then it is not in the returned dictionary.
 *  \returns A new NSDictionary with the keys changed according to the mapping, on optionally with [NSNull null] values removed.
 */
- (NSDictionary *)jcsRemapKeysWithMapping:(NSDictionary *)keyMapping removingNullValues:(BOOL)removeNulls;

@end

NSDictionary+JCSKeyMapping.m

//
//  NSDictionary+JCSKeyMapping.m
//
//  Created by Abizer Nasir on 06/08/2013.
//

#import "NSDictionary+JCSKeyMapping.h"

@implementation NSDictionary (JCSKeyMapping)


- (NSDictionary *)jcsRemapKeysWithMapping:(NSDictionary *)keyMapping removingNullValues:(BOOL)removeNulls {
    __block NSMutableDictionary *newDictionary = [[NSMutableDictionary alloc] initWithCapacity:[self count]];

    [self enumerateKeysAndObjectsUsingBlock:^(id key, id obj, BOOL *stop) {
        if (removeNulls) {
            if ([obj isEqual:[NSNull null]]) return;
        }

        id newKey = keyMapping[key];
        if (!newKey) {
            [newDictionary setObject:obj forKey:key];
        } else {
            [newDictionary setObject:obj forKey:newKey];
        }
    }];

    return [newDictionary copy];
}

@end