write.table writes unwanted leading empty column to header when has rownames

Question

check this example:

> a = matrix(1:9, nrow = 3, ncol = 3, dimnames = list(LETTERS[1:3], LETTERS[1:3]))
> a
  A B C
A 1 4 7
B 2 5 8
C 3 6 9

Answer 1

Citing ?write.table, section CSV files:

By default there is no column name for a column of row names. If col.names = NA and row.names = TRUE a blank column name is added, which is the convention used for CSV files to be read by spreadsheets.

So you must do

write.table(a, 'a.txt', col.names=NA)

and you get

"" "A" "B" "C"
"A" 1 4 7
"B" 2 5 8
"C" 3 6 9