Divide each data frame row by vector in R

Question

I\'m trying to divide each number within a data frame with 16 columns by a specific number for each column. The numbers are stored as a data frame with 1-16 corresponding to

Answer 1

You could use transform

mx2 <- transform(mx, 
    X131.478.1=X131.478.1/sf["X131.478.1",1],
    X131.478.2=X131.478.2/sf["X131.478.2",1],
    etc
)

Quite a bit to type with 16 columns, but it should work.

Answer 2

This is nothing but element-wise matrix multiplication:

mat <- matrix(c(4,2,2,6,7,6, 93,73,88,86,58,65, 123,103,96,128,46,57), nrow=3, byrow=T)

vec = c(1.0660880,0.9104053,0.8642545,0.9611866,0.9711406,1.0560121)

mat %o% 1/vec

           [,1]      [,2]       [,3]       [,4]      [,5]      [,6]
[1,]   3.752035  2.080761   1.876018   6.242284  6.566062  6.242284
[2,] 102.152305 75.169342  96.660246  88.555663 63.707889 66.931606
[3,] 142.319190 97.536761 111.078392 121.210732 53.225063 53.976654

To do that we used the outer-product approach, since directly trying mat %*% 1/vec gives an error on non-conformable arguments because they have different shapes. Or look at the many posts on https://stackoverflow.com/search?q=%5Br%5D+multiply+matrix+by+vector

Answer 3

Just for variety, you could also use mapply

mx <- structure(list(X131.478.1 = c(4L, 93L, 123L), X131.478.2 = c(2L, 
73L, 103L), X131.NSC.1 = c(2L, 88L, 96L), X131.NSC.2 = c(6L, 
86L, 128L), X166.478.1 = c(7L, 58L, 46L), X166.478.2 = c(6L, 
65L, 57L)), .Names = c("X131.478.1", "X131.478.2", "X131.NSC.1", 
"X131.NSC.2", "X166.478.1", "X166.478.2"), class = "data.frame", row.names = c("1/2-SBSRNA4", 
"A1BG", "A1BG-AS1"))

sf <- structure(list(V1 = c(1.066088, 0.9104053, 0.8642545, 0.9611866, 
0.9711406, 1.0560121)), .Names = "V1", row.names = c("X131.478.1", 
"X131.478.2", "X131.NSC.1", "X131.NSC.2", "X166.478.1", "X166.478.2"
), class = "data.frame")


mapply(function(x, y) x * y, mx, t(sf))


    X131.478.1 X131.478.2 X131.NSC.1 X131.NSC.2 X166.478.1 X166.478.2
[1,]   4.264352   1.820811   1.728509    5.76712   6.797984   6.336073
[2,]  99.146184  66.459587  76.054396   82.66205  56.326155  68.640787
[3,] 131.128824  93.771746  82.968432  123.03188  44.672468  60.192690

But for this I think Josh's answer is better... and Gavin's is even better!

Answer 4

Suppose we have a dataframe, df:

> df
  a b   c
1 1 3 100
2 2 4 110

And we want to divide through each row by the same vector, vec:

> vec <- df[1,]
> vec
  a b   c
1 1 3 100

Then we can use mapply as follows:

> mapply('/', df, vec)
     a        b   c
[1,] 1 1.000000 1.0
[2,] 2 1.333333 1.1

Answer 5

sweep is useful for these sorts of operations, but it requires a matrix as input. As such, convert your data frame to a matrix, do the operation and then convert back. For example, some dummy data where we divide each element in respective columns of matrix mat by the corresponding value in the vector vec:

mat <- matrix(1:25, ncol = 5)
vec <- seq(2, by = 2, length = 5)

sweep(mat, 2, vec, `/`)

In use we have:

> mat
     [,1] [,2] [,3] [,4] [,5]
[1,]    1    6   11   16   21
[2,]    2    7   12   17   22
[3,]    3    8   13   18   23
[4,]    4    9   14   19   24
[5,]    5   10   15   20   25
> vec
[1]  2  4  6  8 10
> sweep(mat, 2, vec, `/`)
     [,1] [,2]     [,3]  [,4] [,5]
[1,]  0.5 1.50 1.833333 2.000  2.1
[2,]  1.0 1.75 2.000000 2.125  2.2
[3,]  1.5 2.00 2.166667 2.250  2.3
[4,]  2.0 2.25 2.333333 2.375  2.4
[5,]  2.5 2.50 2.500000 2.500  2.5
> mat[,1] / vec[1]
[1] 0.5 1.0 1.5 2.0 2.5

To convert from a data frame use as.matrix(df) or data.matrix(df), and as.data.frame(mat) for the reverse.