kdb+q-lang

Take a column of a matrix and make it a row in kdb

Consider the matrix:

1 2 3
4 5 6
7 8 9

I'd like to take the middle column, assign it to a variable, and replace the middle row with it, giving me

1 2 3
2 5 8
7 8 9

I'm extracting the middle column using

a:m[;enlist1]

which returns

2
5
8

How do I replace the middle row with a? Is a flip necessary?

Thanks.

Solution

  • You can use dot amend -

    q)show m:(3;3)#1+til 10
    1 2 3
    4 5 6
    7 8 9
q)show a:m[;1]
    2 5 8
q).[m;(1;::);:;a]
    1 2 3
    2 5 8
    7 8 9

    Can see documentation here: