Group and sum values of NSDictionary by month where key is NSDate - ios

Question

I have a dictionary with the following structure,
arrayOne = {
"2015-11-09T00:00:00.000Z" = 1;
"2015-11-16T00:00:00.000Z" = 2;
"2015-11-23T00:00:00.000Z" = 3;
"2015-11-30T00:00:00.000Z" = 4;
"2015-12-07T00:00:00.000Z" = 5;
"2015-12-14T00:00:00.000Z" = 6;
"2015-12-21T00:00:00.000Z" = 7;
"2015-12-28T00:00:00.000Z" = 8;
"2016-01-04T00:00:00.000Z" = 9;
"2016-01-11T00:00:00.000Z" = 1;
"2016-01-18T00:00:00.000Z" = 2;
"2016-01-25T00:00:00.000Z" = 3;
}
I'd like to create another dictionary with values like,
arrayTWo = {
"November" = 10;
"December" = 26;
"January" = 15;
}
I tried by getting month values of dates in a separate array and values in a separate array and then tried to get those in a nsmutabledictionary, but it does not assign value for duplicate keys and got a solution like
arrayTWo = {
"November" = 4;
"December" = 8;
"January" = 3;
}
I couldn't find a better way, Any options are appreciated. Thanks.

Answer 1

Try this, it uses NSDateFormatter to get the month name from the date, it's localized depending on the current locale. If your locale is not english and you need to get the english month names uncomment the line to set the locale explicitly.
The logic is simple:
Enumerate the dictionary, If the key (month) exists, add the value, if it doesn't create the key
NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
formatter.dateFormat = #"MMMM";
// formatter.locale = [NSLocale localeWithLocaleIdentifier:#"en_US_POSIX"];
NSMutableDictionary *result = [NSMutableDictionary dictionary];
for (NSDate *key in arrayOne.allKeys) {
NSString *month = [formatter stringFromDate:key];
if (result[month] == nil) {
result[month] = arrayOne[key];
} else {
NSInteger value = [result[month] integerValue];
result[month] = #(value + [arrayOne[key] integerValue]);
}
}
NSLog(#"%#", result);