How to set unique row and column names of a matrix when its dimension is unknown?

Question

I have matrix like :

     [,1][,2][,3][,4]
[1,]  12  32  43  55
[2,]  54  54  7   8
[3,]  2   56  76  88
[4,]  58  99  93  34

I do not know in advance how many rows and columns I will have in matrix. Thus, I need to create row and column names dynamically.

I can name columns (row) directly like:

colnames(rmatrix) <- c("a", "b", "c", "d")

However, how can I create my names vector dynamically to fit the dimensions of the matrix?

nm <- ("a", "b", "c", "d")
colnames(rmatrix) <- nm 

Answer 1

You can use rownames and colnames and setting do.NULL=FALSE in order to create names dynamically, as in:

set.seed(1)
rmatrix  <-  matrix(sample(0:100, 16), ncol=4)

dimnames(rmatrix) <- list(rownames(rmatrix, do.NULL = FALSE, prefix = "row"),
                          colnames(rmatrix, do.NULL = FALSE, prefix = "col"))

rmatrix
     col1 col2 col3 col4
row1   26   19   58   61
row2   37   86    5   33
row3   56   97   18   66
row4   89   62   15   42

you can change prefix to name the rows/cols as you want to.

Answer 2

To dynamically names columns (or rows) you can try

colnames(rmatrix) <- letters[1:ncol(rmatrix)]

where letters can be replaced by a vector of column names of your choice. You can do similar thing for rows.