Hidden arguments of functional select

In one of my previous posts, I discussed functional form of select, update, exec and delete. If you remember, the general form of a functional select is ?[t;c;b;a] where t is the table, c is for constraints, b for by clause and a for aggregation. Most of the time, you will see only these 4 arguments but functional select can actually have up to 6 arguments!

The full form looks like this:

?[t;c;b;a;n;i]

where n stands for number of rows and i for specific rows you want to extract.

Let’s look at some examples!

t:([];time:5?.z.t;sym:5?`AAPL`MSFT`IBM;price:5?100;size:5?200)

A simple functional select to call the entire table:

q)?[t;();0b;()]
time sym price size
----------------------------
04:54:11.685 MSFT 73 140
13:01:04.698 IBM 90 104
05:18:45.828 IBM 43 10
02:25:54.221 MSFT 90 1
11:32:19.305 AAPL 84 90

If we only want the first two rows, we set n to 2:

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q)?[t;();0b;();2]
time sym price size
----------------------------
04:54:11.685 MSFT 73 140
13:01:04.698 IBM 90 104

To get last two rows, we set n to -2:

q)?[t;();0b;();-2]
time sym price size
----------------------------
02:25:54.221 MSFT 90 1
11:32:19.305 AAPL 84 90

If we only want first and third row, set n to 0W and then, i to 0 2,

q)?[t;();0b;();0W;0 2]
time sym price size
----------------------------
04:54:11.685 MSFT 73 140
05:18:45.828 IBM 43 10

To get first, third and fourth row:

q)?[t;();0b;();0W;0 2 3]
time sym price size
----------------------------
04:54:11.685 MSFT 73 140
05:18:45.828 IBM 43 10
02:25:54.221 MSFT 90 1

Not many people are aware of these two extra arguments so you can use them to impress your colleagues!