Replace all NSNull objects in an NSDictionary

Question

I'm curious, I currently have an NSDictionary where some values are set to an NSNull object thanks to the help of json-framework.

The aim is to strip all NSNull values and replace it with an empty string.

I'm sure someone has done this somewhere? No doubt it is probably a four liner and is simple, I am just far too burnt out to figure this out on my own.

Thanks!

Answer 1

another variation:

NSDictionary * NewDictionaryReplacingNSNullWithEmptyNSString(NSDictionary * dict) {
    NSMutableDictionary * const m = [dict mutableCopy];    
    NSString * const empty = @"";
    id const nul = [NSNull null];
    NSArray * const keys = [m allKeys];
    for (NSUInteger idx = 0, count = [keys count]; idx < count; ++idx) {
        id const key = [keys objectAtIndex:idx];
        id const obj = [m objectForKey:key];
        if (nul == obj) {
            [m setObject:empty forKey:key]; 
        }
    }

    NSDictionary * result = [m copy];
    [m release];
    return result;
}

The result is the same as, and it appears pretty much identical to Jacob's, but the speed and memory requirements are one half to one third (ARC or MRC) in the tests I made. Of course, you could also use it as a category method as well.

Answer 2

Really simple:

@interface NSDictionary (JRAdditions)
- (NSDictionary *)dictionaryByReplacingNullsWithStrings;
@end

@implementation NSDictionary (JRAdditions)

- (NSDictionary *)dictionaryByReplacingNullsWithStrings {
   const NSMutableDictionary *replaced = [self mutableCopy];
   const id nul = [NSNull null];
   const NSString *blank = @"";

   for(NSString *key in self) {
      const id object = [self objectForKey:key];
      if(object == nul) {
         //pointer comparison is way faster than -isKindOfClass:
         //since [NSNull null] is a singleton, they'll all point to the same
         //location in memory.
         [replaced setObject:blank 
                      forKey:key];
      }
   }

   return [replaced copy];
}

@end

Usage:

NSDictionary *someDictThatHasNulls = ...;
NSDictionary *replacedDict = [someDictThatHasNulls dictionaryByReplacingNullsWithStrings];