How to remove column names from a matrix in R?

Question

  M = matrix(1:9,3,3)
colnames(M)=c('a','b','c')

Suppose I have a matrix M , with column names 'a','b','c'. And I want to remove the names, so that M

M    [,1] [,2] [,3]
[1,]    1    4    7
[2,]    2    5    8
[3,]    3    6    9

Rather than

       a     b    c
[1,]    1    4    7
[2,]    2    5    8
[3,]    3    6    9

How do I do this?

Answer 1

I know it's been a while since this was asked, but seeing as it is a highly trafficked question, I thought this might be useful.

If you want to perform this action on M instead of its column names, you could try

M <- unname(M)
>M
     [,1] [,2] [,3]
[1,]    1    4    7
[2,]    2    5    8
[3,]    3    6    9

This would be more efficient if you want to pipe or nest the output into subsequent functions because colnames does not return M.

Answer 2

You can try

colnames(M) <- NULL

Using your example:

> M
#     a b c
#[1,] 1 4 7
#[2,] 2 5 8
#[3,] 3 6 9
> colnames(M) <- NULL
> M
#     [,1] [,2] [,3]
#[1,]    1    4    7
#[2,]    2    5    8
#[3,]    3    6    9

However, if your data is stored in a data.frame instead of a matrix, this won't work. As explained in ?data.frame:

The column names should be non-empty, and attempts to use empty names will have unsupported results

If your data is stored as a data.frame (this can be checked with class(my_data)), you could try to convert it into a matrix with M <- as.matrix(my_data). Hope this helps.