a list of N subsequent elements in KDB

Question

Given the table t: ([] a: 1 2 3 4), how can one obtain the column b for e.g.,

n=2

a b
-----
1 1 2
2 2 3
3 3 4
4 ,4

n=3

a b
-------
1 1 2 3
2 2 3 4
3 3 4
4 ,4

where n is the number of subsequent elements of a (including a) to be included in b.

Answer 1

Use next and scan. The left argument is the number of subsequent elements you want:

q)update b:flip 1 next\a from t
a b
----
1 1 2
2 2 3
3 3 4
4 4
q)update b:flip 2 next\a from t
a b
------
1 1 2 3
2 2 3 4
3 3 4
4 4