Efficient multiplication of columns in a data frame

A data.table solution will avoid lots of internal copying while having the advantages of not spattering the code with $.

 library(data.table)
 DT <- data.table(df)
 DT[ , new := column1 * column2]

As Blue Magister said in comments,

df$new_column <- df$column1 * df$column2

should work just fine. Of course we can never know for sure if we don't have an example of the data.

A minor, somewhat less efficient, version of Sacha's Answer is to use transform() or within()

df <- transform(df, new = column1 * column2)

df <- within(df, new <- column1 * column2)

(I hate spattering my user code with $.)

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