Suppose there are two 1-D arrays of the same length:
let x = fromListUnboxed (ix1 4) [1, 2, 3, 4]
let y = fromListUnboxed (ix1 4) [5, 6, 7, 8]
Now I would like to stack these two arrays into one 2-D array so that these arrays form the rows. How can I do it in repa?
Basically, I'm looking for an equivalent of numpy's row_stack:
>>> x = np.array([1, 2, 3, 4])
>>> y = np.array([5, 6, 7, 8])
>>> np.row_stack((x, y))
array([[1, 2, 3, 4],
[5, 6, 7, 8]])
Note. The two arrays, x and y, come from outside, i.e. I cannot create the 2-D array from scratch.
As I mentioned in the initial comment, all you need is to reshape then append (both in Data.Array.Repa.
ghci> let x' = reshape (ix2 4 1) x
ghci> let y' = reshape (ix2 4 1) y
ghci> z <- computeP $ x' `append` y' :: IO (Array U DIM2 Int)
ghci> z
AUnboxed ((Z :. 4) :. 2) [1,5,2,6,3,7,4,8]
As for pretty-printing, repa isn't very good (likely because there is no good pretty printing for higher dimensions). Here is a one-line hack to display z
ghci> putStr $ unlines [ unwords [ show $ z ! ix2 i j | i<-[0..3] ] | j<-[0..1] ]
1 2 3 4
5 6 7 8