如何將NSDictionarys的NSArray轉換為NSDictionarys的嵌套NSArray

Question

如果我有一個帶有幾個字典對象（每個字典都是一個Person）的NSArray（或可變數組），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 }
]

我如何將其分成四個數組，按姓氏（在姓氏內）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

您可以使用鍵值編碼和謂詞來做一些漂亮的事情。

//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]];
}

只要字典具有@"surname"鍵或Person對象具有-(NSString *)surname方法，這將適用於Person對象（更好）或詞典。

Answer 2

您應該使用專門的Person類，而不是NSDictionary。

---

您可以先將其分組為“字典數組字典”，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;

如果確實需要數組，則可以使用[result allValues] 。

如果需要排序的數組，則需要手動對其進行排序：

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