How do I return an array with the initial letters of all the objects in another array?

Question

I am working on converting a plain tableview to a sectioned tableview. I would like the section titles to be the first letter for the items in the section.

This is what I have so far in my titleForHeaderInSection method:

NSSortDescriptor *sortDescriptor;
sortDescriptor = [[[NSSortDescriptor alloc] initWithKey:@"Name"
             ascending:YES] autorelease];
NSArray *sortedArray;
NSMutableArray *commonNameArray = [tableDataSource valueForKey:@"Name"];

NSArray *uniquearray;
uniquearray = [[NSSet setWithArray:commonNameArray] allObjects];
sortedArray = [uniquearray sortedArrayUsingSelector:@selector(caseInsensitiveCompare:)];

This code removes the duplicate titles and sorts the list alphabetically. Now I just need to convert the strings in the array to the first letters only. What is the best way to go about this?

Answer 1

NSMutableSet *firstCharacters = [NSMutableSet setWithCapacity:0];
for( NSString *string in [tableDataSource valueForKey:@"Name"] )
    [firstCharacters addObject:[string substringToIndex:1]];

NSArray *uniquearray = [[firstCharacters allObjects] sortedArrayUsingSelector:@selector(caseInsensitiveCompare:)];

Answer 2

Thanks for the help. In a rare moment of inspiration I just got it working. Here's what I did. Anyone see anything wrong with doing it this way?

-(NSString *)tableView:(UITableView *)tableView titleForHeaderInSection:(NSInteger)section {
     NSSortDescriptor *sortDescriptor;
     sortDescriptor = [[[NSSortDescriptor alloc] initWithKey:@"CommonName"
    ascending:YES] autorelease];
     NSArray *sortedArray;
     NSMutableArray *commonNameArray = [tableDataSource valueForKey:@"CommonName"];

     NSArray *uniquearray;
     uniquearray = [[NSSet setWithArray:commonNameArray] allObjects];
     sortedArray = [uniquearray sortedArrayUsingSelector:@selector(caseInsensitiveCompare:)];

     NSString *stringForFirstLetter = [[sortedArray objectAtIndex:section] substringToIndex:1];

return stringForFirstLetter;}