[R] help: how to change the column name of data.frame

[wu sz]

Hello,

I have a data frame with 15 variables, and want to exchange the data
of 4th column and 6th column. First I append a column in the data
frame, copy the 4th column data there, then copy the 6th column data
to 4th column, and copy the appended column data to 6th column, but
the names of the 4th and 6th column are still unchanged. How can I
exchange them?

Thank you,
Shengzhe