獲取按其各自的值排序的NSDictionary鍵

Question

我有一個整數值的NSMutableDictionary，我想獲得一個按鍵排列，按各自的值升序排列。例如，用這本字典：

mutableDict = { 
    "A" = 2, 
    "B" = 4, 
    "C" = 3, 
    "D" = 1, 
} 

我想結束與陣列["D", "A", "C", "B"]。當然，我的真實詞典遠遠大於四項。

Answer 1

該NSDictionary方法keysSortedByValueUsingComparator:應該做的伎倆。

你只需要一個返回NSComparisonResult的方法來比較對象的值。

你的字典是

NSMutableDictionary * myDict; 

而且你的陣列是

NSArray *myArray; 

myArray = [myDict keysSortedByValueUsingComparator: ^(id obj1, id obj2) { 

    if ([obj1 integerValue] > [obj2 integerValue]) { 

      return (NSComparisonResult)NSOrderedDescending; 
    } 
    if ([obj1 integerValue] < [obj2 integerValue]) { 

      return (NSComparisonResult)NSOrderedAscending; 
    } 

    return (NSComparisonResult)NSOrderedSame; 
}]; 

只需使用NSNumber對象而不是數字常量。

順便說一句，這是取自： https://developer.apple.com/library/content/documentation/Cocoa/Conceptual/Collections/Articles/Dictionaries.html

Answer 2

NSDictionary有這個叫做allKeys整潔的方法。

如果你想要排序陣列，keysSortedByValueUsingComparator:應該做的伎倆。

理查德的解決方案也適用，但使一些額外的電話，你不一定需要：

// Assuming myDictionary was previously populated with NSNumber values. 
NSArray *orderedKeys = [myDictionary keysSortedByValueUsingComparator:^NSComparisonResult(id obj1, id obj2){ 
    return [obj1 compare:obj2]; 
}]; 

Answer 3

這裏有一個解決方案：

NSDictionary *dictionary; // initialize dictionary 
NSArray *sorted = [[dictionary allKeys] sortedArrayUsingComparator:^NSComparisonResult(id obj1, id obj2) { 
    return [[dictionary objectForKey:obj1] compare:[dictionary objectForKey:obj2]]; 
}]; 

Answer 4

最簡單的辦法：

[dictionary keysSortedByValueUsingSelector:@selector(compare:)]

Answer 5

在這裏我做了這樣的事情：

NSMutableArray * weekDays = [[NSMutableArray alloc] initWithObjects:@"Sunday",@"Monday",@"Tuesday",@"Wednesday",@"Thursday",@"Friday",@"Saturday", nil]; 
NSMutableDictionary *dict = [[NSMutableDictionary alloc] init]; 
NSMutableArray *dictArray = [[NSMutableArray alloc] init]; 

for(int i = 0; i < [weekDays count]; i++) 
{ 
    dict = [NSMutableDictionary dictionaryWithObjectsAndKeys:[NSNumber numberWithInt:i],@"WeekDay",[weekDays objectAtIndex:i],@"Name",nil]; 
    [dictArray addObject:dict]; 
} 
NSLog(@"Before Sorting : %@",dictArray); 

@try 
{ 
    //for using NSSortDescriptor 
    NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"WeekDay" ascending:YES]; 
    NSArray *descriptor = @[sortDescriptor]; 
    NSArray *sortedArray = [dictArray sortedArrayUsingDescriptors:descriptor]; 
    NSLog(@"After Sorting : %@",sortedArray); 

    //for using predicate 
    //here i want to sort the value against weekday but only for WeekDay<=5 
    int count=5; 
    NSPredicate *Predicate = [NSPredicate predicateWithFormat:@"WeekDay <=%d",count]; 
    NSArray *results = [dictArray filteredArrayUsingPredicate:Predicate]; 

    NSLog(@"After Sorting using predicate : %@",results); 
} 
@catch (NSException *exception) 
{ 
    UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Sorting cant be done because of some error" message:[NSString stringWithFormat:@"%@",exception] delegate:self cancelButtonTitle:@"Ok" otherButtonTitles:nil]; 
    [alert setTag:500]; 
    [alert show]; 
    [alert release]; 
}