CODEWITHSUNDEEP
rdata.table
Roger J Bos CFA
Roger J Bos CFA

Reputation: 504

Confused by warning when using the "dot dot prefix" (..) in data.table

I want to sum some columns in a data.table, specifying those columns in a variable. I then use the .. prefix (see New Features data.table 1.10.2) to select those columns. However, this results in a Warning:

mdt <- as.data.table(mtcars)
factorsGEN <- c("disp","hp","drat")
# This works but gives the warning below
mdt[ , score := rowSums(mdt[ , ..factorsGEN])]
#Warning message:
#  In `[.data.table`(mdt, , ..factorsGEN) :
#  Both 'factorsGEN' and '..factorsGEN' exist in calling scope. Please remove 
# the '..factorsGEN' variable in calling scope for clarity.

# This does not work, results in error because factorsGEN is not found
mdt[, score := rowSums(mdt[, factorsGEN])]

I get a warning, which I don't remember getting when I first wrote the code, so it may be the result of an update to the data.table code. Could anyone please tell me how to avoid the warning. I can't figure it out.

Upvotes: 6

Views: 1290

Answers (1)

Richard Layton
Richard Layton

Reputation: 126

You can use .SD and the warning vanishes.

mdt[ , score := rowSums(mdt[ , .SD, .SDcols = factorsGEN])]

Upvotes: 1

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