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Is it possible to write something like this? f as = [ (x, y) | x:xs <- as, y <- xs ] ie a cartesian product that only has unique pairs?
f as = [ (x, y) | x:xs <- as, y <- xs ]
Maybe you need the following?
import Data.List (tails) pairs :: [a] -> [(a, a)] pairs xs = [(x, y) | (x:ys) <- tails xs, y <- ys]
Here's a way to make the question precise in an interesting way:
We know that
let xs = [1..3] in sequence [xs,xs]
evaluates to
[[1,1],[1,2],[1,3],[2,1],[2,2],[2,3],[3,1],[3,2],[3,3]]
What we want are the elements off the diagonal, namely
[[1,2],[1,3],[2,1],[2,3],[3,1],[3,2]]
What function of xs would do that?
xs
Does it generalize to more than two products, the way sequence does?
sequence
Is it possible to write something like this?
f as = [ (x, y) | x:xs <- as, y <- xs ]ie a cartesian product that only has unique pairs?
Maybe you need the following?
Here's a way to make the question precise in an interesting way:
We know that
evaluates to
What we want are the elements off the diagonal, namely
What function of
xswould do that?Does it generalize to more than two products, the way
sequencedoes?