r - Drop data frame columns by name

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I have a number of columns
that I would like to remove from a data frame. I know that we can delete them
individually using something
like:

df$x <-
            NULL

But I was hoping
to do this with fewer commands.

Also, I know
that I could drop columns using integer indexing like
this:

df <- df[
            -c(1, 3:6, 12) ]

But I
am concerned that the relative position of my variables may
change.

Given how powerful R is, I figured there
might be a better way than dropping each column one by one.

Answer

You can use a simple list of names
:

DF <-
            data.frame(

 x=1:10,
 y=10:1,

            z=rep(5,10),
 a=11:20
)
drops <-
            c("x","z")
DF[ , !(names(DF) %in%
            drops)]

Or,
alternatively, you can make a list of those to keep and refer to them by name
:

keeps <- c("y",
            "a")
DF[keeps]

EDIT
:
For those still not acquainted with the drop
argument of the indexing function, if you want to keep one column as a data frame, you
do:

keeps <- "y"
DF[
            , keeps, drop =
            FALSE]

drop=TRUE
(or not mentioning it) will drop unnecessary dimensions, and hence return a vector with
the values of column y.