在一個較小的鍵值編碼數組中使用對象之間的公共鍵 - 值對分割一個NSArray

Question

我試圖找到一個很好的解決方案，以字典數組爲單位，在它們之間鍵入一個常用值的較小字典。
下面是一個例子，我JSON，我從這個開始：

{ 
    "field": [ 
    { 
     "id": 6, 
     "name": "Andrea" 
    }, 
    { 
     "id": 67, 
     "name": "Francesco" 
    }, 
    { 
     "id": 8, 
     "name": "Maria" 
    }, 
    { 
     "id": 6, 
     "name": "Paolo" 
    }, 
    { 
     "id": 67, 
     "name": "Sara" 
    } 
    ] 
} 

我希望得到這樣的結果：

{ 
    "field": [ 
    { 
     "6": [ 
     { 
      "name": "Andrea", 
      "id": 6 
     }, 
     { 
      "name": "Paolo", 
      "id": 6 
     } 
     ], 
     "67": [ 
     { 
      "name": "Sara", 
      "id": 67 
     }, 
     { 
      "name": "Francesco", 
      "id": 67 
     } 
     ], 
     "8": [ 
     { 
      "name": "Maria", 
      "id": 8 
     } 
     ] 
    } 
    ] 
} 

我設法使用此代碼，它的工作原理，但我「M是否存在疑惑的東西更正確，更快捷：

NSArray * array = ...; 
    NSSortDescriptor *sorter1=[[NSSortDescriptor alloc]initWithKey:@"id" ascending:YES selector:@selector(compare:)]; 
    NSSortDescriptor *sorter2=[[NSSortDescriptor alloc]initWithKey:@"name" ascending:YES selector:@selector(caseInsensitiveCompare:)]; 
    NSArray *sortDescriptors=[NSArray arrayWithObjects:sorter1,sorter2,nil]; 
    array = [array sortedArrayUsingDescriptors:sortDescriptors];  
    //////////////////////////////SPLITTER 
    NSMutableArray * subcategorySplittedArray = [[NSMutableArray alloc]initWithCapacity:30]; 
    NSNumber * lastID=[[array objectAtIndex:0]objectForKey:@"id"]; 
    NSMutableArray * shopArray = [[NSMutableArray alloc]initWithCapacity:100]; 
    NSMutableDictionary * catDict = nil; 
    for (NSDictionary * dict in array) { 
     NSNumber * catID = [dict objectForKey:@"id"]; 
     if ([lastID isEqualToNumber:catID]) { 
      [shopArray addObject:dict]; 
     } 
     else { 

      catDict = [[NSMutableDictionary alloc]init ]; 
      [catDict setObject:[shopArray copy] forKey:lastID]; 
      [subcategorySplittedArray addObject:catDict]; 
      [shopArray removeAllObjects]; 
      [shopArray addObject:dict]; 
      lastID = catID; 
     } 
    } 
    catDict = [[NSMutableDictionary alloc]init ]; 
    [catDict setObject:[shopArray copy] forKey:lastID]; 
    [subcategorySplittedArray addObject:catDict]; 
    //////////////////////////////////// 
    return subcategorySplittedArray; 

} 

Answer 1

NSMutableDictionary* result = [NSMutableDictionary dictionary]; 
NSArray* ids = [array valueWithKey:@"id"]; 
NSSet* uniqueIDs = [NSSet setWithArray:ids]; 
for (NSNumber* anID in uniqueIDs) 
{ 
    NSPredicate* pred = [NSPredicate predicateWithFormat:@"id == %@", anID]; 
    NSArray* dictsForID = [array filteredArrayUsingPredicate:pred]; 
    [result setObject:dictsForID forKey:anID]; 
} 

如果有很多的ID，你可以通過建立一個謂語用變量引用的循環之外，然後只需替換變量產生特定ID謂每個通過循環加快這一點。

順便說一句，在你的問題，結果「場」還是出於某種原因的數組。我不認爲它需要。

---

更新，以只有一個通：

NSMutableDictionary* result = [NSMutableDictionary dictionary]; 
for (NSDictionary* dict in array) 
{ 
    NSNumber* anID = [dict objectForKey:@"id"]; 
    NSMutableArray* resultsForID = [result objectForKey:anID]; 
    if (!resultsForID) 
    { 
     resultsForID = [NSMutableArray array]; 
     [result setObject:resultsForID forKey:anID]; 
    } 

    [resultsForID addObject:dict]; 
}