Matrix element division in R

Question

I have a Matrix:

close   close.1 close.2
1   38.050  22.320  23.115
2   37.650  22.150  23.055
3   37.295  22.090  23.090

And I would like to divide "close" by "close.1", "close" by "close.2" and finally "close.1" by "close.2" for each row.

I'm aware that I can write a horrible looking for loop that would solve this but I would be really grateful to know if there was an easy way to do this in R ?

Any help would be greatly appreciated.

Thanks.

Answer 1

What you actually have there is a data frame. It's essentially a matrix, you're right, but you access the columns by using the column's names.

Accessing each column of the data frame can be done through a command like this:

Matrix$close

This should give you the desired data frame, if I understood your question correctly.

New_DataFrame <- data.frame(close = Matrix$close / (Matrix$close.1 * Matrix$close.2), close.1 = Matrix$close.1 / Matrix$close.2)

These operations are all done in respect to each individual row.

If you want your answer in the form of a matrix instead of a data frame, use this:

New_Matrix <- data.matrix(New_DataFrame)

And switching back to a data frame from a matrix is as easy as:

New_DataFrame <- data.frame(New_Matrix)

Hope that helps!

Answer 2

If mat is your matrix, then mat[,1]/mat[,2] gives you the element-wise division of each row. If mat is actually a data.frame not a matrix, then the above works, as does mat$close/mat$close.1 .

Answer 3

> combn(1:3, 2)
     [,1] [,2] [,3]
[1,]    1    1    2
[2,]    2    3    3
> apply(combn(1:3, 2), 2, function(x) mat[, x[1]]/mat[,x[2]] )