Multiply columns in a data frame by a vector

Question

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

Answer 1

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

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Or use sweep

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

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

mapply(`*`, d1, v1)

Answer 2

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

Answer 3

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