Multiply columns in a data frame by a vector

17
votes

What I want to do is multiply all the values in column 1 of a data.frame by the first element in a vector, then multiply all the values in column 2 by the 2nd element in the vector, etc...

c1 <- c(1,2,3)
c2 <- c(4,5,6)
c3 <- c(7,8,9)
d1 <- data.frame(c1,c2,c3)

  c1 c2 c3
1  1  4  7
2  2  5  8
3  3  6  9

v1 <- c(1,2,3)

So the result is this:

  c1  c2  c3
1  1  8   21
2  2  10  24
3  3  12  27

I can do this one column at a time but what if I have 100 columns? I want to be able to do this programmatically.

3
r
Is the entire dataframe numeric? - gung - Reinstate Monica
Not the entire data frame for the problem I'm working on. There is a factor column. - Garry3k
You should include that in your example so that people can take it into account. - gung - Reinstate Monica

3 Answers

13
votes

Or simply diagonalize the vector, so that each row entry is multiplied by the corresponding element in v1:

c1 <- c(1,2,3)
c2 <- c(4,5,6)
c3 <- c(7,8,9)
d1 <- as.matrix(cbind(c1,c2,c3))
v1 <- c(1,2,3)

d1%*%diag(v1)

     [,1] [,2] [,3]
[1,]    1    8   21
[2,]    2   10   24
[3,]    3   12   27
8
votes

We can also replicate the vector to make the lengths equal and then multiply

d1*v1[col(d1)]
#  c1 c2 c3
#1  1  8 21
#2  2 10 24
#3  3 12 27

Or use sweep

sweep(d1, 2, v1, FUN="*")

Or with mapply to multiply the corresponding columns of 'data.frame' and elements of 'vector'

mapply(`*`, d1, v1)
8
votes

Transposing the dataframe works.

c1 <- c(1,2,3)
c2 <- c(4,5,6)
c3 <- c(7,8,9)
d1 <- data.frame(c1,c2,c3)
v1 <- c(1,2,3)
t(t(d1)*v1)
#     c1 c2 c3
#[1,]  1  8 21
#[2,]  2 10 24
#[3,]  3 12 27

EDIT: If all columns are not numeric, you can do the following

c1 <- c(1,2,3)
c2 <- c(4,5,6)
c3 <- c(7,8,9)
d1 <- data.frame(c1,c2,c3)

# Adding a column of characters for demonstration
d1$c4 <- c("rr", "t", "s")

v1 <- c(1,2,3)

#Choosing only numeric columns
index <- which(sapply(d1, is.numeric) == TRUE)
d1_mat <- as.matrix(d1[,index])

d1[,index] <- t(t(d1_mat)*v1)
d1
#  c1 c2 c3 c4
#1  1  8 21 rr
#2  2 10 24  t
#3  3 12 27  s