Drop data frame columns by name

Question

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
<         


        

Answer 1

within(df, rm(x))

is probably easiest, or for multiple variables:

within(df, rm(x, y))

Or if you're dealing with data.tables (per How do you delete a column by name in data.table?):

dt[, x := NULL]   # Deletes column x by reference instantly.

dt[, !"x"]   # Selects all but x into a new data.table.

or for multiple variables

dt[, c("x","y") := NULL]

dt[, !c("x", "y")]

Answer 2

You could use %in% like this:

df[, !(colnames(df) %in% c("x","bar","foo"))]

Answer 3

There's a function called dropNamed() in Bernd Bischl's BBmisc package that does exactly this.

BBmisc::dropNamed(df, "x")

The advantage is that it avoids repeating the data frame argument and thus is suitable for piping in magrittr (just like the dplyr approaches):

df %>% BBmisc::dropNamed("x")

Answer 4

Here is a dplyr way to go about it:

#df[ -c(1,3:6, 12) ]  # original
df.cut <- df %>% select(-col.to.drop.1, -col.to.drop.2, ..., -col.to.drop.6)  # with dplyr::select()

I like this because it's intuitive to read & understand without annotation and robust to columns changing position within the data frame. It also follows the vectorized idiom using - to remove elements.

Answer 5

DF <- data.frame(
  x=1:10,
  y=10:1,
  z=rep(5,10),
  a=11:20
)
DF

Output:

    x  y z  a
1   1 10 5 11
2   2  9 5 12
3   3  8 5 13
4   4  7 5 14
5   5  6 5 15
6   6  5 5 16
7   7  4 5 17
8   8  3 5 18
9   9  2 5 19
10 10  1 5 20

---

DF[c("a","x")] <- list(NULL)

Output:

        y z
    1  10 5
    2   9 5
    3   8 5
    4   7 5
    5   6 5
    6   5 5
    7   4 5
    8   3 5    
    9   2 5
    10  1 5

Answer 6

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.