复制包含多个子字典的字典，并仅从子字典中返回某些键

Question

在我当前的iPhone项目中，我创建了一个字典，它以“名称”键的第一个字母对子字典进行分组。 NSLog返回以下内容。我想创建一个相同的字典，只显示每个首字母键下的“名称”键。在子字典中制作一些项目的最佳方法是什么？ ObjectForKey方法将只选择首字母的项目（例如：“B”或“C”）。如果我没有足够清楚地解释，请告诉我。 谢谢！

sectionedDictionaryByFirstLetter:{ 
B =  (
      { 
     Name = "B...A Name Starting with B"; 
     Image = "ImageName1.png"; 
     Text = "Some Text"; 
    } 
); 
C =  (
      { 
     Name = "C...A Name Starting with C"; 
     Image = "ImageName2.png"; 
     Text = "Some Text"; 
    } 
); 
N =  (
      { 
     Name = "N...A Name Starting with N"; 
     Image = "ImageName3.png"; 
     Text = "Some Text"; 

    }, 
      { 
     Name = "N...A Name Starting with N"; 
     Image = "ImageName4.png"; 
     Text = "Some Text"; 

    }, 
      { 
     Name = "N...A Name Starting with N"; 
     Image = "ImageName5.png"; 
     Text = "Some Text"; 

    } 
    ); 
} 

我在寻找最终的结果是：

sectionedDictionaryByFirstLetter:{ 
B =  (
      { 
     Name = "B...A Name Starting with B"; 
    } 
); 
C =  (
      { 
     Name = "C...A Name Starting with C"; 
    } 
); 
N =  (
      { 
     Name = "N...A Name Starting with N"; 
    }, 
      { 
     Name = "N...A Name Starting with N"; 
    }, 
      { 
     Name = "N...A Name Starting with N"; 
    } 
    ); 
} 

Answer 1

NSMutableDictionary* newDict = [NSMutableDictionary dictionary]; 
for (NSString* key in sectionedDictionaryByFirstLetter) { 
    NSMutableArray* newList = [NSMutableArray array]; 
    [newDict setObject:newList forKey:key]; 
    for (NSDictionary* entry in [sectionedDictionaryByFirstLetter objectForKey:key]) { 
     NSString* name = [entry objectForKey:@"Name"]; 
     [newList addObject:[NSDictionray dictionaryWithObject:name forKey:@"Name"]]; 
    } 
} 

Answer 2

核心基础有很大的作用，CFDictionaryApplyFunction（我希望他们移植的功能NSDictionary太）。但是，NSDictionary和CFDictionary是“免费桥梁”，这意味着您可以免费投射它们。

因此，解决方案是创建一个应用函数SaveName，它将用于上面的CFDictionaryApplyFunction。例如：

void SaveName(const void* key, const void* value, void* context) { 
    NSMutableDictionary* result = (NSMutableDictionary*) context; 
    NSDictionary* dataDict = (NSDictionary*) value; 
    NSString* letterKey = (NSString*) key; 
    [result setObject:[dataDict valueForKey:@"Name"] forKey:@letterKey]; 
} 

void main() { 

    NSDictionary* exampleDict = .. ; 
    NSMutableDictionary* resultDict = [NSMutableDictionary dictionary]; 
    CFDictionaryApplyFunction((CFDictionaryRef)exampleDict, SaveName, (void*)resultDict); 
    // now, the resultDict contains key-value pairs of letter-name! 
} 

我的代码假定“值”字典中只有一个对象。您可以更改SaveName以考虑您自己的数据结构，但这基本上是实现它的方式。