How do I return columns starting with a particular prefix in KDB?

Question

Say for example I have a table:

q)([] aa: til 5; ab: til 5; bb: til 5)

aa ab bb
--------
0  0  0
1  1  1
2  2  2
3  3  3
4  4  4

Is there a simple way of querying for just the columns that begin with a?

Answer 1

If your table is in-memory and unkeyed then take (#) can also do it for you:

{where[c!(c:cols x)like"a*"]#x}t

But Matts solution is more general and thus more useful!

Answer 2

You can use functional select

?[t;();0b;{x!x}cols[t] where cols[t] like "a*"]

https://code.kx.com/q/basics/funsql/