Question

I need to extract parts of a dataframe, using the values which I have generated previously. For example, I have the following data:

a<-c(1,2,3,4,6,7,10,12,17,20)
df1<-data.frame(a)

I then want to exclude these values (in “a” in df1) from df2 when they appear in column b:

b<-c(1,2,3,4,5,6,6,6,7,8,9,10,11,11,11,12,13,14,14:20)
c<-c(1:25)
df1<-data.frame(b,c)

So, I should be left with a dataframe with rows 5,8,9,11 etc…

Can anyone help me out with the code to remove these values from my dataframe (df1).

Many thanks.

Answer 1

subset() will be a good friend to you for this sort of thing:

subset(df1, !b %in% a)

(The sub-expression b %in% a tests each element of b to determine whether or not it is in a, returning a vector of TRUEs and FALSEes. !b %in% a just negates/flips those Boolean values, so that you end up with a logical vector indexing with TRUEs the rows of df1 that you would like to keep (i.e. those that don’t appear in a).)