Returns true for the first value of the group according to the ordering. The group is optional; when a group is provided, the function returns true once per group.
Examples
table T = with
[| as N, as G |]
[| 0, "b" |]
[| 3, "a" |]
[| 2, "a" |]
[| 1, "a" |]
T.A = argfirst() sort T.N
T.B = argfirst() by T.G sort T.N
show table "" with
T.N
T.G
T.A
T.B