Hello,
I don't understand the question.
Like this?
xx <- "B"
yy <- "D"
a[xx, on = v]
a[c(xx, yy), on = v]
Note that .(xx, yy) doesn't work. It outputs something else.
Could you give an example of more complicated expressions you have
doubts with?
Hope this helps,
Rui Barradas
Às 14:10 de 21/02/2019, Pascal A. Niklaus escreveu:
I am converting data.frame-based code to data.table, for performance
reasons.
Is there a way to refer to columns using expressions in the "i"-part?
Here is an example:
a <- data.table(x=rep(LETTERS[1:10],each=2), y=1:20)
v <- "x"
For the j-part, I can access the column whose name is stored in v as
a[,..v]
However, for the i-part I did not find a good way to achieve the same.
For a simple case, the following works
xx <- "B"
a[xx, on=v]
However, I can't see how this is easily expanded to more complex logical
expressions.
Pascal
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