using mean with .SD and .SDcols in data.table

Question

I am writing a very simple function to summarize columns of data.tables. I am passing one column at a time to the function, and then doing some diagnostics to figure out th

Answer 1

I think the appropriate way of approaching what you want is to just use the standard syntax:

dt[ , lapply(.SD, mean), .SDcols = "a"]

Alternatively, you can pass a variable by name as follows:

col_to_pass = "a"
dt[ , mean(get(col_to_pass)) ]

Eventually, you can generalized this approach to multiple columns as follows:

col_to_pass = c("a", "d")
dt[ , lapply( mget(col_to_pass), mean) ]