How can I get an array of the indexes from another array that has been sorted?

Question

I want to sort an array by its objets and then get the indexes like so:

NSMutableArray *myArray = [[NSMutableArray alloc] initWithObjects: @"3", @"2", @"1", @"0", @"1", @"2", nil];

I want the indexes of the objects in ascending order. Here, because the lowest value has an index of 3, the indexes would be would be: 3, 2, 4, 1, 5, 0 or something like that.

Any ideas?

Thanks!

Answer 1

just sort it and use indexOfObject:. Like so:

NSArray *sorted = [myArray sortedArrayUsingSelector: @selector(compare:)];
NSMutableArray *indices = [NSMutableArray array];
for (id object in myArray)
  [indices addObject: [NSNumber numberWithInteger: [sorted indexOfObject: object]]];

(Out of my head, hope this works.)

Answer 2

hello,

You can also use below of the code, May its useful to you,

    NSSortDescriptor *_lastDescriptor = [[NSSortDescriptor alloc] initWithKey:@"" ascending:YES];
NSArray *_lastArray = [NSArray arrayWithObject:_lastDescriptor];


firstCharacterArray = (NSMutableArray *)[[nameIndexesDictionary allKeys] sortedArrayUsingDescriptors:_lastArray];
//firstCharacterArray = (NSMutableArray *)[[nameIndexesDictionary allKeys] sortedArrayUsingSelector:@selector(localizedCaseInsensitiveCompare:)];
for (NSString *eachlastIndex in firstCharacterArray)
{
    NSSortDescriptor *lastDescriptor = [[NSSortDescriptor alloc] initWithKey:@""
                                                                   ascending:YES];
    //selector:@selector(localizedCaseInsensitiveCompare:)] ;
    NSArray *descriptorslast = [NSArray arrayWithObject:lastDescriptor];
    [[nameIndexesDictionary objectForKey:eachlastIndex] sortUsingDescriptors:descriptorslast];
    [lastDescriptor release];
}

Answer 3

Here's what I ended up doing:

//Create a mutable array of the indexes in the myArray (just a list from 0...n)

NSMutableArray *indexes = [[NSMutableArray alloc] init];

for (int i = 0; i < myArray.count; i++){
    [indexes addObject: [NSNumber numberWithInteger:i]];
}

//Create a dictionary with myArray as the objects and the indexes as the keys
NSDictionary *tempDictionary = [NSDictionary dictionaryWithObjects:myArray forKeys:indexes];

//Create an array of myArray's keys, in the order they would be in if they were sorted by the values 
NSArray *sorted = [tempDictionary keysSortedByValueUsingSelector: @selector(compare:)];