Question

I’m trying to get a following target value by using NSPredicate.

But, I’m having difficulty using NSPredicate syntax.

I want to get lastname lists of max age of same names in source data without duplicate.

Please anyone’s help…

NSDictionary *dic1 = [NSDictionary dictionaryWithObjects:@[@"James",    @10] forKeys:@[@"LastName", @"Age"]];
NSDictionary *dic2 = [NSDictionary dictionaryWithObjects:@[@"Robert",   @15] forKeys:@[@"LastName", @"Age"]];
NSDictionary *dic3 = [NSDictionary dictionaryWithObjects:@[@"Robert",   @10] forKeys:@[@"LastName", @"Age"]];
NSDictionary *dic4 = [NSDictionary dictionaryWithObjects:@[@"James",    @20] forKeys:@[@"LastName", @"Age"]];
NSDictionary *dic5 = [NSDictionary dictionaryWithObjects:@[@"David",    @20] forKeys:@[@"LastName", @"Age"]];
NSDictionary *dic6 = [NSDictionary dictionaryWithObjects:@[@"Walter",   @30] forKeys:@[@"LastName", @"Age"]];
NSDictionary *dic7 = [NSDictionary dictionaryWithObjects:@[@"Nicholas", @30] forKeys:@[@"LastName", @"Age"]];
NSDictionary *dic8 = [NSDictionary dictionaryWithObjects:@[@"David",    @30] forKeys:@[@"LastName", @"Age"]];
NSDictionary *dic9 = [NSDictionary dictionaryWithObjects:@[@"David",    @30] forKeys:@[@"LastName", @"Age"]];

NSArray *persons = [NSArray arrayWithObjects:dic1, dic2, dic3, dic4, dic5, dic6, dic7, dic8, dic9, nil];

NSPredicate *predicate = [NSPredicate predicateWithFormat:???]

NSArray *result = [persons filteredArrayUsingPredicate:predicate];
NSLog(@"result : %@",result);



source data
LastName          age
James              10
Robert             15
Robert             10
James              20
David              20
Walter             30
Nicholas           30
David              30
David              30

target data
James              20
Robert             15
David              30
Walter             30
Nicholas           30

Answer 1

I don’t believe this can be done with a predicate. I would do it by sorting the array with the key “Age”, and then looping through that array, adding the first record to a results array, then checking whether the next record has the same LastName as the first, and if so don’t add that one to the final array. Like this:

NSArray *sorters = [NSArray arrayWithObject:[NSSortDescriptor sortDescriptorWithKey:@"Age" ascending:NO]];
    NSArray *sorted = [persons sortedArrayUsingDescriptors:sorters];
    NSMutableArray *result = [NSMutableArray array];
    for (id dict in sorted) {
        if (! [[result valueForKey:@"LastName"] containsObject:[dict valueForKey:@"LastName"]]) {
            [result addObject:dict];
        }
    }
    NSLog(@"%@",result);