如何将 NSDictionarys 的 NSArray 转换为 NSDictionarys 的嵌套 NSArray

Question

如果我有一个带有多个字典对象（每个字典都是一个人）的 NSArray （或可变数组），如下所示：

[
  { forename: chris, surname: smith, age: 22 }
  { forename: paul, surname: smith, age: 24 }
  { forename: dave, surname: jones, age: 21 }
  { forename: alan, surname: jones, age: 26 }
  { forename: cecil, surname: reeves, age: 32 }
  { forename: pablo, surname: sanchez, age: 42 }
]

我如何将其分成四个数组的数组，按姓氏（并在该名字内）排序，如下所示：

[
    [ 
      { forename: alan, surname: jones, age: 26 }
      { forename: dave, surname: jones, age: 21 }
    ]
    [  
      { forename: cecil, surname: reeves, age: 32 }
    ]
    [
      { forename: pablo, surname: sanchez, age: 42 }
    ]
    [ 
      { forename: chris, surname: smith, age: 22 }
      { forename: paul, surname: smith, age: 24 }
    ]
]

Answer 1

您可以使用键值编码和谓词做一些非常简洁的事情...

//retrieve an array of the distinct surnames
NSArray * distinctSurnames = [peopleArray valueForKeyPath:@"@distinctUnionOfObjects.surname"];
//at this point, if you need the surnames in a specific order, you can do so here.

NSMutableArray * groupedPeople = [NSMutableArray array];

//for each of the surnames...
for (NSString * surname in distinctSurnames) {
  //create a predicate to only find people with this surname
  NSPredicate * filter = [NSPredicate predicateWithFormat:@"surname = %@", surname];
  //retrieve only the people with this surname and add them to the final array
  [groupedPeople addObject:[peopleArray filteredArrayUsingPredicate:filter]];
}

这适用于 Person 对象（这会更好）或字典，只要字典有 >@"surname" 键或 Person 对象有一个 -(NSString *)surname 方法。

Answer 2

您应该使用专门的 Person 类，而不是 NSDictionary。

---

您可以首先将其分组为字典数组的字典，例如，

NSMutableDictionary* result = [NSMutableDictionary dictionary];
for (Person* person in peopleArray) {
    NSString* surname = person.surname;
    NSMutableArray* surnameArray = [result objectForKey:surname];
    if (surnameArray == nil) {
        [result setObject:[NSMutableArray arrayWithObject:person]
                   forKey:surname]; 
    } else {
        [surnameArray addObject:person];
    }
}
return result;

如果您确实需要一个数组，则可以使用[result allValues]。

如果需要排序数组，则需要手动排序：

NSArray* sortedSurnames = [[result allKeys] sortedArrayUsingSelector:@selector(compare:)];
return [result objectsForKeys:sortedSurnames notFoundMarker:[NSNull null]];