Apologies for a question that probably makes it obvious that I usually work in Python/pandas, but I'm stuck with this. How do I select a
data.table column using a string?
dt$"string" dt$as.name("string") dt$get("string")
I'm sure this is super simple, but I'm not getting it. Any help is greatly appreciated!
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After some of the helpful comments and tips below, I think I've narrowed down the problem a bit and have a reproducible example. Consider:
dt = data.table(ID = c("a","a","a","b","b","b"), col1=rnorm(6), col2=rnorm(6)*100)
And assume we want to assign the values in
col1. As I've learned below, the
data.table syntax for this would be
dt[,col1:=col2], clean and simple. The problems start when one (or both) of the variables in the
j argument are strings. I found the following:
dt[, "col1":=col2] works as expected
dt[, "col1":="col2"] fails as expected (tries to assign the character
col2 to the double vector
dt[, "col1":=get("col2")] works as expected
dt[, get("col1")] returns
col1 as expected
dt[, get("col1"):=col2] or any other assignment fails.
Some context: the reason for doing this is that I'm constructing strings in a loop, to access a larger number of columns that are all named
colname_colnumber, i.e. I loop over
colnumber to then access column