Matrices in R Programming

Question

I am new to R programming, and I have few questions regarding matrices in R.

I have a function that returns a matrix. I want to check if the returned matrix is empty or not. How do I check it in R? If it is an integer, we can check it by is.null(someinteger). But how do we check the same in the case of matrices?

Also, an integer can be initialized by x <- NULL. If I have just wanted to initialize a matrix. Do we initialize like mat <- matrix() or is there any other way? mat can be of any size.

Answer 1

If your only concern is that your function returns a matrix then regardless of what your preceding data types/structures are you could always just finalize the output as a matrix unless you need the preceding data processing to work with a matrix structure, which doesn't sound the like problem at all.

see fundamental example below:

x <- c(1:5)
y <- c(6:10)

foo <- function(x, y){
  z <- cbind(x,y)
   return(as.matrix(z))
}

z <-foo(x,y)
z

Answer 2

There is some question of what is meant by "empty" here but this will test if matrix m has zero length:

length(m) == 0

Regarding initializing a matrix this initializes it to be a 0x0 matrix:

m <- matrix(, 0, 0)

and this initalizes it to be a 1x1 matrix containing NA:

m <- matrix()

and this initializes it to an nr by nc matrix of NA values:

m <- matrix(, nr, nc)

Not clear whether any of these are actually useful. You may want to describe what you are trying to accomplish. Why do you need to initialize it at all?

Answer 3

Try:

all(is.na(m))

Or:

is.logical(m)

Can act as a single function test. If one numeric or character is an element of the list, it will return FALSE. The second solution should work; it appears that your function is creating matrices with numbers and/or NAs.