NSArray sort and isolate - iphone

Question

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 aplhabetically 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?

Answer 1

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:)];
}

Answer 2

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"];
}];

Answer 3

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.