Error spliting NSarray into sections - iphone

Question

Okay so I have been working through an example that closely matches what I am trying to achive, the sole difference being that in the example he is directly calling from his database the data he needs to be sectioned etc. Where as I already have a sorted NSArray.
This is the tutorial I am working off - iPhone Development: Creating Native Contacts like screen
I have created a Method that is capturing each entry in the NSArray and putting these results into a alpha based NSDictionary (so their will be a NSDictionary for A,B,C... etc)
here is my method.
//method to sort array and split for use with uitableview Index
- (IBAction)startSortingTheArray:(NSMutableArray *)arrayData
{
//Sort incoming array alphabetically
//sortedArray = [arrayData sortedArrayUsingSelector:#selector(localizedCaseInsensitiveCompare:)];
[self setSortedArray:[arrayData sortedArrayUsingSelector:#selector(localizedCaseInsensitiveCompare:)]];
arrayOfCharacters = [[NSMutableArray alloc]init];
objectsForCharacters = [[NSMutableDictionary alloc]init];
for(char c='A';c<='Z';c++)
{
if([sortedArray count] >0)
{
[arrayOfCharacters addObject:[NSString stringWithFormat:#"%c",c]];
[objectsForCharacters setObject:sortedArray forKey:[NSString stringWithFormat:#"%c",c]];
NSLog(#"%#", objectsForCharacters);
}
[sortedArray release];
//Reloads data in table
[self.tableView reloadData];
}
}
This is putting every value into every alpha section, I am hoping someone can help me with making it so that only alpha sections are established if there is a value in the array for it.. then only loading those values into each section, not every section.

Answer 1

This piece of code will do just that and will be much more efficient than filtering the array once for each letter.
//Sort incoming array alphabetically so that each sub-array will also be sorted.
NSArray *sortedArray = [arrayData sortedArrayUsingSelector:#selector(localizedCaseInsensitiveCompare:)];
// Dictionary will hold our sub-arrays
NSMutableDictionary *arraysByLetter = [NSMutableDictionary dictionary];
// Iterate over all the values in our sorted array
for (NSString *value in sortedArray) {
// Get the first letter and its associated array from the dictionary.
// If the dictionary does not exist create one and associate it with the letter.
NSString *firstLetter = [value substringWithRange:NSMakeRange(0, 1)];
NSMutableArray *arrayForLetter = [arraysByLetter objectForKey:firstLetter];
if (arrayForLetter == nil) {
arrayForLetter = [NSMutableArray array];
[arraysByLetter setObject:arrayForLetter forKey:firstLetter];
}
// Add the value to the array for this letter
[arrayForLetter addObject:value];
}
// arraysByLetter will contain the result you expect
NSLog(#"Dictionary: %#", arraysByLetter);
Note that arraysByLetter is a dictionary that contains one array per "first letter" that exists in your initial data.
--- Added on 2011-09-23 ---
[sortedArray removeAllObjects];
NSArray *sortedKeys = [arraysByLetter.allKeys sortedArrayUsingSelector:#selector(localizedCaseInsensitiveCompare:)];
for (NSString *key in sortedKeys) {
[sortedArray addObject:key];
[sortedArray addObjectsFromArray: [arraysByLetter objectForKey:key]];
}
NSLog(#"Sorted Array: %#", sortedArray);
The output is the following:
C,
Computer,
H,
Helene,
Hello,
J,
Jules,
W,
World

Answer 2

Looks like you need to filter sortedArray with a predicate for each letter. Something like this...
for(char c='A';c<='Z';c++) {
NSPredicate *predicate =
[NSPredicate predicateWithFormat:#"SELF beginswith[c] '%c'", c];
NSArray *objectsBeginningWithCurrentLetter = [array filteredArrayUsingPredicate:predicate];
if([sortedArray count] >0)
{
[arrayOfCharacters addObject:[NSString stringWithFormat:#"%c",c]];
if ([objectsBeginningWithCurrentLetter count] > 0) {
[objectsForCharacters setObject:objectsBeginningWithCurrentLetter forKey:[NSString stringWithFormat:#"%c",c]];
NSLog(#"%#", objectsForCharacters);
}
}
[sortedArray release];
//Reloads data in table
[self.tableView reloadData];
}