How to sort in descending order using multiple comparison fields in Kotlin

Question

Kotlin allows me to sort ASC and array using multiple comparison fields.

For example:

return ArrayList(originalItems)     .sortedWith(compareBy({ it.localHits }, { it.title })) 

But when I try sort DESC (compareByDescending()), it does not allow me to use multiple comparison fields.

Is there any way I can do it?

Answer 1

You could use the thenByDescending() (or thenBy() for ascending order) extension function to define a secondary Comparator.

Assuming originalItems are of SomeCustomObject, something like this should work:

return ArrayList(originalItems)         .sortedWith(compareByDescending<SomeCustomObject> { it.localHits }                 .thenByDescending { it.title }) 

(of course you have to replace SomeCustomObject with your own type for the generic)

Answer 2

You can also just use sort ASC and then reverse it:

return ArrayList(originalItems).sortedWith(compareBy({ it.localHits }, { it.title })).asReversed() 

The implementation of the asReversed() is a view of the sorted list with reversed index and has better performance than using reverse()