add two columns using indexes in data.table in R

Question

I have a data table containing 4 variables. How can I add two columns using indexes.

As an example:

DT = data.table(a=6,b=8,c=0,d=5)
min1 = 3
min2 = 4
DT[,"mrg":=min1+min2,with=F] # How to  write this line correctly
DT[,(c(min1,min2)):=NULL] # this works

It's generally discouraged to refer to cols by number. See, for example, the answer to the first question in the FAQ https://rawgit.com/wiki/Rdatatable/data.table/vignettes/datatable-faq.html — Frank, Nov 04 '16 at 15:12

score 3 · Accepted Answer · answered Nov 04 '16 at 11:44

3

You can use .SDcols:

DT[, "mrg" := Reduce("+", .SD), .SDcols = c(min1, min2)]

answered Nov 04 '16 at 11:44

Roland

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add two columns using indexes in data.table in R

1 Answers1