How to know a dimension of matrix or vector in R?

Question

I want to find the function in R which does the same as the function size in Matlab.

In Matlab, if A = [ 1 2 3 4 5], then size(A) = 1 5.

If A =[ 1 2 3;4 5 6], then size(A) = 3 3.

In R, I found that the function dim gives the size of a matrix, but it doesn't apply to vectors.

Please help me solve this problem.

Thanks a lot.

Answer 1

Try dim(A) it's equal to Matlab size(A) function

Answer 2

As you noted dim doesn't work on vectors. You can use this function which will take any number of vectors matrices, data.frames or lists and find their dimension or length:

DIM <- function( ... ){
    args <- list(...)
    lapply( args , function(x) { if( is.null( dim(x) ) )
                                    return( length(x) )
                                 dim(x) } )
}

# length 10 vector
a <- 1:10
# 3x3 matrix
b <- matrix(1:9,3,3)
# length 2 list
c <- list( 1:2 , 1:100 )
# 1 row, 2 column data.frame
d <- data.frame( a =1 , b = 2 )


DIM(a,b,c,d)
#[[1]]
#[1] 10

#[[2]]
#[1] 3 3

#[[3]]
#[1] 2

#[[4]]
#[1] 1 2