如何将 NSDictionarys 的 NSArray 变成 NSDictionarys 的嵌套 NSArray

Posted 2023-02-23

【中文标题】如何将 NSDictionarys 的 NSArray 变成 NSDictionarys 的嵌套 NSArray

【英文标题】：How to turn NSArray of NSDictionarys into a nested NSArray of NSDictionarys

【发布时间】：2010-10-21 17:51:29

【问题描述】：

如果我有一个包含多个字典对象（每个字典都是一个 Person）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 
]

我如何将它分成一个由四个数组组成的数组，按姓氏排序（并在该名字内），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 
    ]
]

【参考方案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]];

这将适用于 Person 对象（会更好）或字典，只要字典具有 @"surname" 键或 Person 对象具有 -(NSString *)surname 方法。

【讨论】：

很棒的解决方案！没有足够的人使用 KVC。真的很漂亮。

【参考方案2】：

您应该使用专门的 Person 类，而不是 NSDictionary。

---

您可以先将其分组为字典数组字典，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;

如果你真的需要一个数组，你可以使用[result allValues]。

如果需要排序数组，需要手动排序：

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