Multiplying all columns in dataframe by single column

Question

I know it is a basic quaestion but couldnt find any solution to it. I want to multiply all columns of a dataframe by single column.

df1<-data.frame(F1=c(1,5,8,9),F2=c(1,5,8,9),F3=c(1,5,8,9))
> df1
  F1 F2 F3
1  1  1  1
2  5  5  5
3  8  8  8
4  9  9  9

C<-data.frame(C=c(2,1,2,0.5))
> C
    C
1 2.0
2 1.0
3 2.0
4 0.5

I wanna multiply each column of df1 by C. I have tried:

df2<-df1[,c(1:3)]*C[,1]
df2<-df1*C
df2< df1%*%C
and
for(i in 2:length(names(b))) {
+     df2 <- C[, 1] * b[, i]
+ }

Thanks!

Answer 1

Also try

df1 * t(C)
#    F1   F2   F3
#1  2.0  2.0  2.0
#2  5.0  5.0  5.0
#3 16.0 16.0 16.0
#4  4.5  4.5  4.5

---

When we try to multiply data frames they must be of the same size.

df1 * C

error in Ops.data.frame(df1, C) : ‘*’ only defined for equally-sized data frames

t() turns C into a matrix, i.e. a vector with dimension attribute of length 4. This vector gets recycled when we multiply it with df1.

What would also work in the same way (and might be faster than transposing C):

df1 * C$C

or

df1 * unlist(C)

Answer 2

We can vectorize the multiplication by replicating the 'C' column

df1 * C[row(df1)]
#     F1   F2   F3
#1  2.0  2.0  2.0
#2  5.0  5.0  5.0
#3 16.0 16.0 16.0
#4  4.5  4.5  4.5

Or use the rep explicitly

df1 * rep(C$C, ncol(df1))