[Jprogramming] Length errors when getting multiple columns from array

[Jon Hough]

I have a 2-d array. e.g.
arr =: 10 6 $ i. 10 
I want to get the first 3 columns from the array, e.g.  3{."1and get the first 4 elements, e.g. 4{."1
However, combining these, as in
3 4 {."(0 1) arrgives a length error. Of course 3{. and 4{.  will give different shape results so should be boxed and then concatenated perhaps(?). I am not sure how to do this, but the end result I want would be something like:

┌─────┐

│0 1 2│

│6 7 8│

│2 3 4│

│8 9 0│

│4 5 6│

│0 1 2│

│6 7 8│

│2 3 4│

│8 9 0│

│4 5 6│

└─────┘


concatenated with


┌───────┐│0 1 2 3││6 7 8 9││2 3 4 5││8 9 0 1││4 5 6 7││0 1 2 3││6 7 8 9││2 3 4 5││8 9 0 1││4 5 6 7│












└───────┘