Apply a list of parameters to a list of input

[powerpeanuts]

Hi, I have a simple question:

I have a list b:(1 5 6;9 10 76; 43 12 11) and I would like to take the nth indexed element from each list where n is a list, for example n = (0;2;1).

So the output should be (1;76;12).

What is the easiest syntax to do it? Thanks.

[eohara_kdb]

Here's one option:

q)b:(1 5 6;9 10 76; 43 12 11)
q)n:(0;2;1)
q){x y}'[b;n]
1 76 12

[rocuinneagain · Accepted solution]

q)b@'(0;2;1)
1 76 12

[eohara_kdb]

As far as I know it's not possible without some kind of each, so here's the same approach for a table:

q)tab:([time:10:03:54.347 10:04:05.827]price:(20.83 21.44 26.83 29.83e;88.88 88.75 83.27 823.77f);n:0 1)
q)update m:{x y}'[price;n] from tab
time        | price                    n m
------------| ---------------------------------
10:03:54.347| 20.83 21.44 26.83 29.83  0 20.83e
10:04:05.827| 88.88 88.75 83.27 823.77 1 88.75

[cillianreilly]

The lambda isn't necessary here:

q)update m:price@'n from tab
time        | price                    n m
------------| ---------------------------------
10:03:54.347| 20.83 21.44 26.83 29.83  0 20.83e
10:04:05.827| 88.88 88.75 83.27 823.77 1 88.75

Not useful for the general case, but here you can forgo the explicit n column and use the virtual index column instead:

q)tab:([time:10:03:54.347 10:04:05.827]price:(20.83 21.44 26.83 29.83e;88.88 88.75 83.27 823.77f))
q)update m:price@'i from tab
time        | price                    m
------------| -------------------------------
10:03:54.347| 20.83 21.44 26.83 29.83  20.83e
10:04:05.827| 88.88 88.75 83.27 823.77 88.75