This multiplies column n by 2 but what if we wanted to multiply it by the column named n2 and further in this example we only have one n but in a real example we might have many columns and their 2 counterpart. If we could retrieve the name or index of _ then we could find out that the current column is column n and then construct column name n2 from that and then reference it.
xan range 3 | xan map "n+n as n2" | xan transform 0 "2*_"
n,n2
0,0
2,2
4,4
This multiplies column n by 2 but what if we wanted to multiply it by the column named n2 and further in this example we only have one n but in a real example we might have many columns and their 2 counterpart. If we could retrieve the name or index of _ then we could find out that the current column is column n and then construct column name n2 from that and then reference it.