There is a very easy way to reorder the column order or a data frame, but it seems to be unknown from many R users.
Having a data frame named test like
a b c d e [1,] 1 11 21 31 41 [2,] 2 12 22 32 42 [3,] 3 13 23 33 43 [4,] 4 14 24 34 44 [5,] 5 15 25 35 45
all that is required is to reassign the data frame using a new column order, like
new_column_order <- c("b", "c", "a", "e", "d")
test <- test[,new_column_order]
And that solves the problem.
This works both with a data frame and a matrix.