Btibert3 Btibert3 - 4 months ago 17
R Question

Drop data frame columns by name

I have a number of columns that I would like to drop from a data frame. I know that we can drop 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.

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