Sort array into dictionary

Question

I have and array of many strings. I wan't to sort them into a dictionary, so all strings starting the same letter go into one array and then the array becomes the value for a key; the key would be the letter with which all the words in it's value's array begin.

Example

Key = "A" >> Value = "array = apple, animal, alphabet, abc ..."
Key = "B" >> Value = "array = bat, ball, banana ..."

How can I do that? Thanks a lot in advance!

Answer 1

NSArray *list = [NSArray arrayWithObjects:@"apple, animal, bat, ball", nil];
NSMutableDictionary *dict = [NSMutableDictionary dictionary];
for (NSString *word in list) {
    NSString *firstLetter = [[word substringToIndex:1] uppercaseString];
    NSMutableArray *letterList = [dict objectForKey:firstLetter];
    if (!letterList) {
        letterList = [NSMutableArray array];
        [dict setObject:letterList forKey:firstLetter];
    }
    [letterList addObject:word];
}
NSLog(@"%@", dict);

Answer 2

You can achieve what you want through the following steps:

1. Create an empty but mutable dictionary.
2. Get the first character.
3. If a key for that character does not exist, create it.
4. Add the word to the value of the key (should be an NSMutableArray).
5. Repeat step #2 for all keys.

Here is the Objective-C code for these steps. Note that I am assuming that you want the keys to be case insensitive.

// create our dummy dataset
NSArray * wordArray = [NSArray arrayWithObjects:@"Apple", 
                       @"Pickle", @"Monkey", @"Taco", 
                       @"arsenal", @"punch", @"twitch", 
                       @"mushy", nil];
// setup a dictionary
NSMutableDictionary * wordDictionary = [[NSMutableDictionary alloc] init];
for (NSString * word in wordArray) {
    // remove uppercaseString if you wish to keys case sensitive.
    NSString * letter = [[word substringWithRange:NSMakeRange(0, 1)] uppercaseString];
    NSMutableArray * array = [wordDictionary objectForKey:letter];
    if (!array) {
        // the key doesn't exist, so we will create it.
        [wordDictionary setObject:(array = [NSMutableArray array]) forKey:letter];
    }
    [array addObject:word];
}
NSLog(@"Word dictionary: %@", wordDictionary);