An Important Question About NSDictionaries

Question

I have an NSDictionary with NSStrings

Some of the valueForKey:@"Key" have no entry so it's (null)

NSMutableString* addressDictionaryToString = [NSMutableString string];  // use mutable string!
for (NSDictionary* item in address) {     // use fast enumeration!
        [addressDictionaryToString appendFormat:@"%@, %@, %@, %@",
         [item objectForKey:@"Street"],         
         [item objectForKey:@"City"],
         [item objectForKey:@"State"],
         [item objectForKey:@"ZIP"]
         ];
    NSLog(@"MutableString: %@", addressDictionaryToString);
}

So I want to build an NSMutableString but filter out those keys that are null. Any ideas?

UPDATE:::::

Basically I want my resulting String to look like

1 Infinite Loop, Cupertino, CA, 95014 (IF all fields are available)

If Im missing the Street then

Cupertino, CA, 95014

If I'm missing the State then

1 Infinite Loop, Cupertino, 95014

If I only have the state then it should print

CA

(notice that there are no commas on the last element)

Answer 1

How about checking if there's a value for the key?

NSMutableString * addressDictionaryToString = [NSMutableString string];
for (NSDictionary * item in address)
{
    if ([item objectForKey:@"Street"])
        [addressDictionaryToString appendFormat:@"%@, ", 
         [item objectForKey:@"Street"]];
    if ([item objectForKey:@"City"])
        [addressDictionaryToString appendFormat:@"%@, ", 
         [item objectForKey:@"City"]];
    if ([item objectForKey:@"State"])
        [addressDictionaryToString appendFormat:@"%@, ", 
         [item objectForKey:@"State"]];
    if ([item objectForKey:@"ZIP"])
        [addressDictionaryToString appendFormat:@"%@, ", 
         [item objectForKey:@"ZIP"]];
    NSLog(@"MutableString: %@", addressDictionaryToString);
}

The thing is, in your last question, you said your goal was to create a CSV file. It's not technically valid CSV if your rows have varying numbers of fields with no reliable way to identify each one.

Instead, you might try this:

NSMutableString * addressDictionaryToString = [NSMutableString string];
for (NSDictionary * item in address)
{
    [addressDictionaryToString appendFormat:@"%@,", 
     ([item objectForKey:@"Street"]) ? [item objectForKey:@"Street"] : @"" ];
    // ...
    NSLog(@"MutableString: %@", addressDictionaryToString);
}

It checks for the presence of a value and inserts that value if there is one, or just an empty string (resulting in "value,value,,value..."). Also remember there shouldn't be a space after the comma, so I've removed that from this example.

Answer 2

Not exactly sure what you're trying to do but this:

NSDictionary *d=[NSDictionary dictionaryWithObject:[NSNull null] forKey:@"ns"];
NSString *n=[@"Steve " stringByAppendingFormat:@"%@",[d objectForKey:@"ns"]];
NSLog(@"%@",n);

... prints:

Steve <null>

If the key itself does not exist then it will throw an exception when you try to get the value for the nonexistent key. The only recourse in this instance is to check for the key in each dictionary before trying to use it to retrieve a value.