NSDictionary sort by keys as floats

Question

Hi there

basically I have an NSDictionary with keys and values.

The keys are all numbers, but at the moment they are strings.

I want to be able to compare them as numbers in order to sort them.

eg: If I have a Dictionary like this:

{
  "100"  => (id)object,
  "20"   => (id)object,
  "10"   => (id)object,
  "1000" => (id)object,
}

I want to be able to sort it like this:

{
  "10"   => (id)object,
  "20"   => (id)object,
  "100"  => (id)object,
  "1000" => (id)object,
}

Any ideas?

Thanks

Tom

Answer 1

Use compare:options: with NSNumericSearch.

Answer 2

Not sure what you are up to – dictionaries are inherently unsorted, there is no stable key ordering in the default implementation. If you want to walk the values by sorted keys, you can do something like this:

NSInteger floatSort(id num1, id num2, void *context)
{
    float v1 = [num1 floatValue];
    float v2 = [num2 floatValue];
    if (v1 < v2)
        return NSOrderedAscending;
    else if (v1 > v2)
        return NSOrderedDescending;
    else
        return NSOrderedSame;
}

NSArray *allKeys = [aDictionary allKeys];
NSArray *sortedKeys = [allKeys sortedArrayUsingFunction:floatSort context:NULL];
for (id key in sortedKeys)
    id val = [aDictionary objectForKey:key];
    …

Answer 3

Already on SO:

http://stackoverflow.com/questions/2696354/how-can-i-sort-an-nsdictionary (and other similar questions)

Answer 4

You can't sort a dictionary, but you can get the keys as an array, sort that, then output in that order. sortedArrayUsingComparator will do that, and you can compare the strings with the NSNumericSearch option.

NSArray* keys = [myDict allKeys];
NSArray* sortedArray = [keys sortedArrayUsingComparator:^(id a, id b) { 
    return [a compare:b options:NSNumericSearch]; 
}]; 

for( NSString* aStr in sortedArray ) {
    NSLog( @"%@ has key %@", [myDict objectForKey:aStr], aStr );
}