Question

I have a Mutable Dictionary that I removed an element from with removeObjectForKey. That’s fine, but when I enumerate thru the Dictionary, there is a ‘hole’ for the element I deleted. So when I print the Dictionary, it displays that element as (null).

Is there way to ‘pack’ the dictionary after removing an element? I need contiguous numbers for the keys. Example:

BEFORE DELETE:

key:1 value:red
key:2 value:green
key:3 value:blue
key:4 value:yellow

myDictionary removeObjectForKey:2

CURRENT:

key:1 value:red
key:3 value:blue
key:4 value:yellow

DESIRED:

key:1 value:red
key:**2** value:blue
key:**3** value:yellow

Code to remove nil entry from NSMutableDictionary. This is what I came up with, but it is not working:

int count = dictFaves.count;
int x = 1;  // Dictionaries are 1-relative
while ( x <= count ) {

   // get the current row
   NSString *curRow = [NSString stringWithFormat:@"%d", x];
   NSString *temp = [dictFaves objectForKey:curRow];

   // is this row empty? if so, we have found our hole to plug
   if ( temp == nil ) {
       // copy the Fave from the 'next' row to the 'current' row. Effectively   
       //   shifting it 1 lower in the Dictionary
       NSString *nextRow = [NSString stringWithFormat:@"%d", x + 1];
       temp = [dictFaves objectForKey:nextRow];
       [dictFaves setObject:temp forKey:[NSNumber numberWithInt:x]];

       // one final thing to cleanup: remove the old 'next' row. 
       // It has been moved up 1 slot (along with all others)
       [dictFaves removeObjectForKey:[NSString stringWithFormat:@"%d", x+1]];
   }
   x = x + 1;
}

Answer 1

That happens because the NSDictionary (and its mutable subclass) acts like a hash/map/associative array. If you want to keep the indices running consecutively, you have to either reset them after removing an object, or just store everything in a NSMutableArray.