Getting NSDictionary keys sorted by their respective values - objective-c

Question

I have an NSMutableDictionary with integer values, and I'd like to get an array of the keys, sorted ascending by their respective values. For example, with this dictionary:
mutableDict = {
"A" = 2,
"B" = 4,
"C" = 3,
"D" = 1,
}
I'd like to end up with the array ["D", "A", "C", "B"]. My real dictionary is much larger than just four items, of course.

Answer 1

The NSDictionary Method keysSortedByValueUsingComparator: should do the trick.
You just need a method returning an NSComparisonResult that compares the object's values.
Your Dictionary is
NSMutableDictionary * myDict;
And your Array is
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;
}];
Just use NSNumber objects instead of numeric constants.
BTW, this is taken from:
https://developer.apple.com/library/content/documentation/Cocoa/Conceptual/Collections/Articles/Dictionaries.html

Answer 2

NSDictionary has this neat method called allKeys.
If you want the array to be sorted though, keysSortedByValueUsingComparator: should do the trick.
Richard's solution also works but makes some extra calls you don't necessarily need:
// Assuming myDictionary was previously populated with NSNumber values.
NSArray *orderedKeys = [myDictionary keysSortedByValueUsingComparator:^NSComparisonResult(id obj1, id obj2){
return [obj1 compare:obj2];
}];

Answer 3

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

Answer 4

The simplest solution:
[dictionary keysSortedByValueUsingSelector:#selector(compare:)]

Answer 5

Here i have done something like this:
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];
}