NSDictionary Objective-C

Question

I'm trying to store data in the following fashion with a string as the key and I would like an array as the value.

key objects

"letters" {'a','b','c','d'}
"numbers" {1,2,3,4,5,6,7}

Is this possible with NSDictionary in code? If so how would that look like? I'm really confused on this.

Answer 1

You can represent them as property-lists. Property-List Documentation.

<dict>
    <key>letters</key>
    <array>
        <string>a</string>
        <string>b</string>
        <string>c</string>
        <string>d</string>
    </array>
    <key>letters</key>
    <array>
        <integer>1</integer>
        <integer>2</integer>
        <integer>3</integer>
        <integer>4</integer>
        <integer>5</integer>
        <integer>6</integer>
        <integer>7</integer>
    </array>
 </dict>

For an overview of how to serialize and de-serialize your data in Cocoa, see Archives and Serialization Guide for Cocoa

Answer 2

A simple way to do this in code (and just one of many several ways you could do it):

NSMutableDictionary *dict = [NSMutableDictionary dictionary];
[dict setObject:[NSArray arrayWithObjects:@"a", @"b", @"c", @"d", nil] forKey:@"letters"];
[dict setObject:[NSArray arrayWithObjects:[NSNumber numberWithInt:1], [NSNumber numberWithInt:2], [NSNumber numberWithInt:3], [NSNumber numberWithInt:4], nil] forKey:@"numbers"];

That creates an NSDictionary with an array of strings and an array of NSNumber objects, there are other ways to create arrays, but that demonstrates a basic way to do it.

Per the comments below:

If you wanted to add items to the arrays one at a time...

  // create the dictionary and add the letters and numbers mutable arrays
  NSMutableDictionary *dict = [NSMutableDictionary dictionary];
  NSMutableArray *letters = [NSMutableArray array];
  NSMutableArray *numbers = [NSMutableArray array];
  [dict setObject:letters forKey:@"letters"];
  [dict setObject:numbers forKey:@"numbers"];

  // add a letter and add a number
  [[dict objectForKey:@"letters"] addObject:@"a"];
  [[dict objectForKey:@"numbers"] addObject:[NSNumber numberWithInt:1]];  
  // This now has an NSDictionary (hash) with two arrays, one of letters and one 
  // of numbers with the letter 'a' in the letters array and the number 1 in 
  // the numbers array

Answer 3

Assuming you have an NSArray called letters and one called numbers containing the correct values:

NSDictionary* dict = [NSDictionary dictionaryWithObjectsAndKeys:
    letters, @"letters",
    numbers, @"numbers",
    nil
];

Make sure to retain if you want to keep dict around, or alternatively use alloc and initWithObjectsAndKeys.

See NSDictionary API reference for more details.