iPhone, How can I store a value and a key and lookup by key and index?

I've tried NSMutableDictionary however I don't seem to be able to get an object by index.

Any ide开发者_高级运维as?

EDIT: I've trying to create a uitableview sections object, which will store the header titles and be able to increment a counter for the rows. I need to be able to get the counter by index, counter value by title value.

Simplest way is to use 2 collections: dictionary for section infos (row numbers, countries etc) and array for section titles.

NSMutableDictionary *sectionInfos;
NSMutableArray *sectionTitles;

When you need a section info by sectionTitle:

NSDictionary *info = [sectionInfos objectForKey:sectionTitle];
int rowsCount = ((NSArray *)[info objectForKey:@"Countries"]).count;

When you need a section info by sectionIndex:

NSString *title = [sectionTitles objectAtIndex:sectionIndex];
NSDictionary *info = [sectionInfos objectForKey:title];
int rowsCount = ((NSArray *)[info objectForKey:@"Countries"]).count;

When you add a section, add sections info:

[sectionInfos setObject:info forKey:sectionTitle];

and a title to array, so infos and titles will be in sync.

[sectionTitles addObject:sectionTitle];

UPDATE: if the only info needed for section is number of rows: UPDATE2: added types.

NSMutableDictionary *sectionRowCounts;
NSMutableArray *sectionTitles;

Rows count by sectionTitle:

int rowCount = [[sectionRowCounts objectForKey:sectionTitle] intValue];

Rows count by sectionIndex:

NSString *title = [sectionTitles objectAtIndex:sectionIndex];
int rowCount = [[sectionRowCounts objectForKey:title] intValue];

Adding a section:

[sectionRowCounts setObject:[NSNumber numberWithInt:rowCount] forKey:sectionTitle];
[sectionTitles addObject:sectionTitle];

Dictionaries are not ordered; therefore the objects in them do not have an index.

http://developer.apple.com/library/ios/#documentation/cocoa/reference/foundation/Classes/NSDictionary_Class/Reference/Reference.html#//apple_ref/occ/cl/NSDictionary

You need to use the key to retrieve a particular object from a dictionary. If you need to have the objects in a specific order, then you would probably use NSArray instead.

UPDATE

In your edit, you don't show what tableSectionArray is, but it looks like it's a dictionary (which makes it poorly named). You should use an NSArray, not an NSDictionary, to store what you want. If you need more than one value to be stored, then store an object that contains the values you need. Create a class that has the required values as properties; or, if appropriate, add NSDictionary objects to your array. (Based on how you are trying to assign an element from tableSectionArray, it looks like you do want it to contain dictionaries.) But you need the tableSectionArray itself to be an NSArray.

Yes, keep trying with NSMutableDictionary. It's the data structure you need for that. Can you post your code to see why it's not returning the value you expect?

Example:

NSString *yourvalue = @"Hello!";
NSMutableDictionary *d;
[d setValue:yourvalue forKey:@"yourkey"];
NSString *retrievedvalue = [d valueForKey:@"yourkey"];
// you should get value here