NSArray sort and isolate

I have an NSArray of names, I want to sort them alphabetically into a UITableView and separate them into sections.

I have a tagged section at the top, being section 0. I want the names sorted aplh开发者_JAVA技巧abetically to come after that. So all names beginning with A get put into section 1, B into section 2, and so on.

I need to be able to somehow get the number of rows for each section, and then put the objects in each section.

How do I do this?

---

Here is a method for a category on NSArray to do grouping:

@interface NSArray (Grouping)
- (NSArray*) groupUsingFunction: (id (*)(id, void*)) function context: (void*) context;
@end

@implementation NSArray (Grouping)
- (NSArray*) groupUsingFunction: (id (*)(id, void*)) function context: (void*) context
{
    NSArray* groupedArray = nil;

    NSMutableDictionary* dictionary = [NSMutableDictionary new];
    if (dictionary != nil)
    {
        for (id item in self)
        {
            id key = function(item, context);
            if (key != nil)
            {
                NSMutableArray* array = [dictionary objectForKey: key];
                if (array == nil) {
                    array = [NSMutableArray arrayWithObject: item];
                    if (array != nil) {
                        [dictionary setObject: array forKey: key];
                    }
                } else {
                    [array addObject: item];
                }
            }
        }

        groupedArray = [NSMutableArray arrayWithArray: [dictionary allValues]];
        [dictionary release];
    }

    return groupedArray;
}
@end

You can use it like this:

id GroupNameByFirstLetter(NSString* object, void* context)
{
    return [object substringToIndex: 1];
}

NSInteger SortGroupedNamesByFirstLetter(id left, id right, void* context)
{
    return [[left objectAtIndex: 0] characterAtIndex: 0] - [[right objectAtIndex: 0] characterAtIndex: 0];
}

NSMutableArray* names = [NSArray arrayWithObjects: @"Stefan", @"John", @"Alex",
    @"Sue", @"Aura", @"Mikki", @"Michael", @"Joe", @"Steve", @"Mac", @"Fred",
    @"Faye", @"Paul", nil];

// Group the names and then sort the groups and the contents of the groups.

groupedNames_ = [[names groupUsingFunction: GroupNameByFirstLetter context: nil] retain];

[groupedNames_ sortUsingFunction: SortGroupedNamesByFirstLetter context: nil];

for (NSUInteger i = 0; i < [groupedNames_ count]; i++) {
    [[groupedNames_ objectAtIndex: i] sortUsingSelector: @selector(compare:)];
}

---

I modified St3fans answer to be a bit more modern and work with Blocks instead:

@interface NSArray (Grouping)
- (NSArray*) groupUsingBlock:(NSString* (^)(id object)) block;
@end


- (NSArray*) groupUsingBlock:(NSString* (^)(id object)) block
{
    NSArray* groupedArray = nil;

    NSMutableDictionary* dictionary = [NSMutableDictionary new];
    if (dictionary != nil)
    {
        for (id item in self)
        {
            id key = block(item);
            if (key != nil)
            {
                NSMutableArray* array = [dictionary objectForKey: key];
                if (array == nil) {
                    array = [NSMutableArray arrayWithObject: item];
                    if (array != nil) {
                        [dictionary setObject: array forKey: key];
                    }
                } else {
                    [array addObject: item];
                }
            }
        }

        groupedArray = [NSMutableArray arrayWithArray: [dictionary allValues]];
        [dictionary release];
    }

    return groupedArray;
}

You can use it like this:

NSArray *grouped = [arrayToGroup groupUsingBlock:^NSString *(id object) {
        return [object valueForKey:@"name"];
}];

---

You should probably create an array of arrays, one for each letter, and store your names that way. While you can use a single array for storage, there's no quick way to do the segmentation you're looking for. Sorting, sure, but not section-ization.