reduce() hstack python

Question

I am trying to use reduce() function to create a function hstack() which horizontally stacks multiple arrays. As a simple example, lets say

>>>>M=eye((4))
>>>>M
    array([[ 1.,  0.,  0.,  0.],
    [ 0.,  1.,  0.,  0.],
    [ 0.,  0.,  1.,  0.],
    [ 0.,  0.,  0.,  1.]])

>>>>hstack([M,M])
array([[ 1.,  0.,  0.,  0.,  1.,  0.,  0.,  0.],
   [ 0.,  1.,  0.,  0.,  0.,  1.,  0.,  0.],
   [ 0.,  0.,  1.,  0.,  0.,  0.,  1.,  0.],
   [ 0.,  0.,  0.,  1.,  0.,  0.,  0.,  1.]])

This works as I want. Now I define

>>>> hstackm = lambda *args: reduce(hstack, args)

And try to do the hstack() from the previous case

>>>>hstackm([M,M])  
[array([[ 1.,  0.,  0.,  0.],
   [ 0.,  1.,  0.,  0.],
   [ 0.,  0.,  1.,  0.],
   [ 0.,  0.,  0.,  1.]]),
 array([[ 1.,  0.,  0.,  0.],
   [ 0.,  1.,  0.,  0.],
   [ 0.,  0.,  1.,  0.],
   [ 0.,  0.,  0.,  1.]])]

Which is incorrect. How do I define hstackm() to obtain a proper output?

My final objective will be to create a hstackm() function to stack SPARSE matrices if it is possible. Something like,

hstackm = lambda *args: reduce(sparse.hstack, args).

The _*args_ would be csr or _lil_matrix_

thank you

Answer 1

In [16]: hstackm = lambda args: reduce(lambda x,y:hstack((x,y)), args)

In [17]: hstackm([M,M])
Out[17]: 
array([[ 1.,  0.,  0.,  0.,  1.,  0.,  0.,  0.],
       [ 0.,  1.,  0.,  0.,  0.,  1.,  0.,  0.],
       [ 0.,  0.,  1.,  0.,  0.,  0.,  1.,  0.],
       [ 0.,  0.,  0.,  1.,  0.,  0.,  0.,  1.]])