Efficient multiplication of columns in a data frame

Question

I have a large data frame in which I am multiplying two columns together to get another column. At first I was running a for-loop, like so:

for(i in 1:nrow(df)){
    df$new_column[i] <- df$column1[i] * df$column2[i]
}

but this takes like 9 days.

Another alternative was plyr, and I actually might be using the variables incorrectly:

new_df <- ddply(df, .(column1,column2), transform, new_column = column1 * column2)

but this is taking forever

Answer 1

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.