キーを変換しつつ新しいNSDictionaryを返すやつ

NSDictionary+MBUtil.h

#import <Foundation/Foundation.h>

@interface NSDictionary (MBUtil)

- (instancetype)initWithDictionary:(NSDictionary *)dictionary withKeyDictionary:(NSDictionary *)keyDictionary;
+ (instancetype)dictionaryWithDictionary:(NSDictionary *)dictionary withKeyDictionary:(NSDictionary *)keyDictionary;

@end

NSDictionary+MBUtil.m

#import "NSDictionary+MBUtil.h"

@implementation NSDictionary (MBUtil)

- (instancetype)initWithDictionary:(NSDictionary *)dictionary withKeyDictionary:(NSDictionary *)keyDictionary
{
    __block NSMutableDictionary *mutableDictionary = [NSMutableDictionary dictionaryWithCapacity:dictionary.count];
    
    [keyDictionary enumerateKeysAndObjectsUsingBlock:^(id oldKey, id newKey, BOOL *stop) {
        mutableDictionary[newKey] = dictionary[oldKey];
    }];
    
    return [self initWithDictionary:mutableDictionary];
}

+ (instancetype)dictionaryWithDictionary:(NSDictionary *)dictionary withKeyDictionary:(NSDictionary *)keyDictionary
{
    return [[self alloc] initWithDictionary:dictionary withKeyDictionary:keyDictionary];
}

@end