Question

Here’s a simplified version of the 3 data sets I have:

Set A = [1, 1, 2, 2, 1, 2, 2, 1]
Set B = [2, 2, 1, 2, 2, 1, 1, 3]
Set C = [8, 4, 4, 4, 4, 9, 8, 4]

Does Haskell have any built in features for finding unspecified patterns between data sets? I’d like to run my program over 2 or more data sets, and have it report back which ones are similar, which, in this case, would be sets A and B.

Answer 1

If you are not talking about finding consequent intersection.

For each 2 lists we can use intersect function from Data.List, which takes intersection of them.

So, idea is to calculate intersection of all list and sort them.

> snd . last . sort $ [ (length $ intersect x y, (x,y)) | let list = [[1,1,2,2,1,2,2,1],[2,2,1,2,2,1,1,3],[8,4,4,4,4,9,8,4]], x <- list, y <- list, x /= y ]
([1,1,2,2,1,2,2,1],[2,2,1,2,2,1,1,3])

If you are interested in founding the consequent intersection, you can use something like that:

import Data.List (sort, subsequences)

intersectCons :: (Ord a) => [a] -> [a] -> [a]
intersectCons x y = snd . last . sort $
  [ (length x1, x1) | x1 <- subsequences x
                    , x2 <- subsequences y
                    , x1 == x2 ]

For example:

> intersectCons [1, 1, 2, 2, 1, 2, 2, 1] [2, 2, 1, 2, 2, 1, 1, 3]
[2,2,1,2,2,1]

Also we can use it for finding most similar pair of lists:

> snd . last . sort $ [ (length $ intersectCons x y, (x,y)) | let list = [[1,1,2,2,1,2,2,1],[2,2,1,2,2,1,1,3],[8,4,4,4,4,9,8,4]], x <- list, y <- list, x /= y ]
([2,2,1,2,2,1,1,3],[1,1,2,2,1,2,2,1])

Actually, if you want to get not only one pair of lists, but all pairs that are “similar”, you can remove snd . last . sort $ and get all of them.