Question

I get a return array by json,

[{"date": "2011-01-01", "title": "aaa"},
 {"date": "2011-01-01", "title": "bbb"},
 {"date": "2011-01-01", "title": "ccc"},
 {"date": "2011-01-02", "title": "ddd"},
 {"date": "2011-01-02", "title": "eee"},
 {"date": "2011-01-03", "title": "fff"},
 {"date": "2011-01-03", "title": "ggg"}]

I use these code to get the value:

NSDictionary *jsonDictionary = [jsonArray objectAtIndex:i];
NSString *date = [jsonDictionary objectForKey:@"dispalyDate"];
NSString *title = [jsonDictionary objectForKey:@"title"];

The problem is how can I restructure the array or create new array according to the same date, such as

date = 2011-01-01
aaa、bbb、ccc

date = 2011-01-02
ddd、eee

date = 2011-01-03
fff、ggg

Answer 1

Something like this…

NSMutableDictionary *titlesByDate = [NSMutableDictionary dictionary];
for (NSDictionary *entry in jsonDictionary) {
    NSString *date = [entry objectForKey:@"date"];
    NSMutableArray *titles = [titlesByDate objectForKey:date];
    if (!titles) {
        titles = [NSMutableArray array];
        [titlesByDate setObject:titles forKey:date];
    }
    [titles addObject:[entry objectForKey:@"title"]];
}

Now you have a dictionary where the keys are date strings and the values are title arrays. If you really want an array result, you can then do this:

NSMutableArray *array = [NSMutableArray array];
for (NSString *date in titlesByDate) {
    [array addObject:[NSDictionary dictionaryWithObjectsAndKeys:
        date, @"date",
        [titlesByDate objectForKey:date], @"titles",
        nil];
}