Sorting an NSArray using another NSArray as a guide

Question

So, imagine you have a couple of arrays, Colors and Shapes, like this:

Colors: {
Yellow,
Blue,
Red
}

Shapes: {
Square,
Circle,
Diamond
}

Now, if I want to sort Colors into alphabetical order I can do something like this:

NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:nil ascending:YES selector:@selector(localizedCompare:)]; 
NSArray *sortedColors = [colors sortedArrayUsingDescriptors:[NSArray arrayWithObject:sortDescriptor]];
[sortDescriptor release];

But how would I sort the Shapes into the same order that I re-ordered Colors. I don't mean put Shapes into alphabetical order - I mean put Shapes into Colors' alphabetical order...?

Daniel Dickison · Accepted Answer · 2010-10-21 20:27:38Z

9

Easiest way is probably this:

 NSDictionary *dict = [NSDictionary dictionaryWithObjects:colors forKeys:shapes];
 NSArray *sortedShapes = [dict keysSortedByValueUsingSelector:@selector(localizedCompare:)];

answered Oct 21, 2010 at 20:27

Daniel Dickison

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1 Comment

Daniel Dickison Over a year ago

dreamlax's answer is definitely the "cleaner" and more general solution (works with any number of arrays, not just two). I think of this one as more of a quick hack.

dreamlax · Accepted Answer · 2010-10-21 20:29:46Z

If the colours are paired with the arrays, perhaps you should consider using just one array instead of two. For example, you could structure your data in a way that allows you to query both the shape and colour of an object using a single index. There are at least a couple of ways to achieve this.

Use an array of dictionaries, each dictionary contains two key-value pairs, ShapeKey and ColourKey. Once you have established this structure, you can use:

NSSortDescriptor *sd = [[NSSortDescriptor alloc] initWithKey:@"ColourKey" ascending:YES];
NSArray *sortedByColours = [colours sortedArrayUsingDescriptors:[NSArray arrayWithObject:sd];
[sd release];

Define a custom class with two properties, colour and shape. If you use this approach, you can use the code above but simply replace @"ColourKey" with @"colour" (or whatever you chose to call that property).

If you insist on maintaining two separate arrays, go with @Daniel Dickison's answer.

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