Multiply multiple columns in a data frame with specific values from another data frame

2
votes

Think about the following two data frames

df1 <- data.frame(a = rep(1, 10), b = rep(1, 10), c = rep(1, 10))
df2 <- data.frame(company = c("a", "b", "c"), weight = c(5, 10, 20))

df1

   a b c
1  1 1 1
2  1 1 1
3  1 1 1
4  1 1 1
5  1 1 1
6  1 1 1
7  1 1 1
8  1 1 1
9  1 1 1
10 1 1 1

df2

  company weight
1       a      5
2       b     10
3       c     20

I'm now looking for a solution that looks for the column names of df1 in the company column of df2 and multiplies each row of the corresponding company in df1 with the value from the weight column.

So what I want to achieve is:

df.weighted

   a.weighted b.weighted c.weighted
1           5         10         20
2           5         10         20
3           5         10         20
4           5         10         20
5           5         10         20
6           5         10         20
7           5         10         20
8           5         10         20
9           5         10         20
10          5         10         20

Does anyone have an idea?

Thank you!

1
r

1 Answers

4
votes

We could make the lengths of both the datasets same and multiply

out <- setNames(df2$weight, df2$company)[col(df1)] * df1
names(out) <- paste0(names(out), ".weighted")

Or another option is

df1 * split(df2$weight, df2$company)[names(df1)]

Or with match

df2$weight[match(names(df1), df2$company)][col(df1)] * df1

Or using sweep

sweep(df1[df2$company],  2, FUN = `*`, df2$weight)