.Q.ft[x;y]

Where

• y is a keyed table
• x is a unary function x[t] in which t is a simple table

returns a table with at least as many key columns as t.

As an example, note that you can index into a simple table with row indices, but not into a keyed table – for that you should use a select statement. However, to illustrate the method, we show an indexing function being applied to a keyed table.

q)\l sp.q

q)sp 2 3           / index simple table with integer list argument
s  p  qty
---------
s1 p3 400
s1 p4 200

q)s 2 3            / index keyed table fails
'length

Now create an indexing function, and wrap it in .Q.ft. This works on both types of table:

q).Q.ft[{x 2 3};s]
s | name  status city
--| -------------------
s3| blake 30     paris
s4| clark 20     london

Equivalent select statement:

q)select from s where i in 2 3
s | name  status city
--| -------------------
s3| blake 30     paris
s4| clark 20     london