Split nsarray to nsdictionary

Question

I am quering Parse and get an array back

PFQuery *query = [Points query];
[query whereKey:@"city" equalTo:[SharedParseStore sharedStore].chosenCity];
query.cachePolicy = kPFCachePolicyCacheThenNetwork;

I want to sort the array into a dictionary based on the district value that is in the Point object so that i can use a tableview with sections (district section names)

[query findObjectsInBackgroundWithBlock:^(NSArray *objects, NSError *error) {
    if (!error) {
    NSMutableDictionary *dict = [[NSMutableDictionary alloc]init];

    for (Points *point in objects) {
        [dict setValue:point forKey:point.district];
    }            
        block(dict, error);
    } else {

        NSLog(@"Error: %@ %@", error, [error userInfo]);
    }
}];

The problem is it only adds 1 value of course

So to make it easy to understand: The objects coming from Parse are Point objects with the following property's: Name,District,City

I want to create a NSdictionary with the districts (so I need to collect them out of the objects first because I don't know them) as a key and the value for that key is an array with the points that are in that district.

I don't know beforehand what the districts will be. They will need to be picked from the objects array that is returned from Parse.

My final object I want to create is a nsdictionary with arrays of points for every distinct district(that is the key).

Example: [@"districtA" : an array with Point objects that have districtA in their district property, etc etc]

what is the best way to do this because i really can't see how to do it ?

Answer 1

You answered your own question when you say:

I want to create a NSdictionary with the districts as a key and the value for that key is an array with the points that are in that district.

[query findObjectsInBackgroundWithBlock:^(NSArray *objects, NSError *error) {
    if (!error) {
        NSMutableDictionary *dict = [@{} mutableCopy];

        for (Points *point in objects) {
            // if no point for that district was added before,
            // initiate a new array to store them
            if (![dict containsKey:point.district])
                dict[point.district] = [@[] mutableCopy];

            [dict[point.district] addObject:point];
        }     

        block(dict, error);

    } else {
        NSLog(@"Error: %@ %@", error, [error userInfo]);
    }
}];