How to sort a list of lists in lexicographic order?

Question

I want to sort the elements of a Haskell list in lexicographic order, Is there any method?

Before sorted:

[ [], [1,2], [1], [1,2,3], [2], [1,3], [2,3], [3]]

After sorted:

[ [], [1], [1,2], [1,2,3], [1,3], [2], [2,3], [3]]

I hate to sound rude, but did it not occur to just search for something like "Haskell sort list"? — Thomas M. DuBuisson, Jan 27 '14 at 04:50
Most straightforward approach: just define function lex_compare :: String -> String -> Ordering which compares two lists according desired order then use sortBy function. — user3974391, Jan 27 '14 at 04:50
@user2894391: Somebody has thought ahead: http://hackage.haskell.org/package/base-4.4.0.0/docs/src/GHC-Classes.html#line-189 — Niklas B., Jan 27 '14 at 04:52
@NiklasB. Yes, you're right. But maybe OP wanted some explanation of how does this work? — user3974391, Jan 27 '14 at 04:55

score 4 · Accepted Answer · answered Jan 27 '14 at 04:48

4

The default Ord instance for lists actually works that way:

Prelude> import Data.List
Prelude Data.List> sort [ [], [1,2], [1], [1,2,3], [2], [1,3], [2,3], [3]]
[[],[1],[1,2],[1,2,3],[1,3],[2],[2,3],[3]]

answered Jan 27 '14 at 04:48

Niklas B.

1 Answers1