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我试图通过使用 NSPredicate 来获得以下目标值。

但是，我在使用 NSPredicate 语法时遇到了困难。

我想获取源数据中同名的最大年龄的姓氏列表而不会重复。

请任何人的帮助...

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
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1 回答 1

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我不相信这可以用谓词来完成。我会通过使用键“Age”对数组进行排序，然后循环遍历该数组，将第一条记录添加到结果数组中，然后检查下一条记录是否具有与第一条相同的 LastName，如果是，请不要t 将那个添加到最终数组中。像这样：

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);
于 2012-08-21T15:31:21.170 回答