Remove last N rows in data frame with the arbitrary number of rows

Question

I have a data frame and I want to remove last N rows from it. If I want to remove 5 rows, I currently use the following command, which in my opinion is rather convoluted:

df<- df[-seq(nrow(df),nrow(df)-4),] 

How would you accomplish task, is there a convenient function that I can use in R?

In unix, I would use:

tac file | sed '1,5d' | tac  

Answer 1

head with a negative index is convenient for this...

df <- data.frame( a = 1:10 ) head(df,-5) #  a #1 1 #2 2 #3 3 #4 4 #5 5 

p.s. your seq() example may be written slightly less(?) awkwardly using the named arguments by and length.out (shortened to len) like this -seq(nrow(df),by=-1,len=5).

Answer 2

This one takes one more line, but is far more readable:

n<-dim(df)[1] df<-df[1:(n-5),] 

Of course, you can do it in one line by sticking the dim command directly into the re-assignment statement. I assume this is part of a reproducible script, and you can retrace your steps... Otherwise, strongly recommend in such cases to save to a different variable (e.g., df2) and then remove the redundant copy only after you're sure you got what you wanted.