Minus operation of data frames

Question

I have 2 data frames df1 and df2.

df1 <- data.frame(c1=c("a","b","c","d"),c2=c(1,2,3,4) ) df2 <- data.frame(c1=c("c","d","e","f"),c2=c(3,4,5,6) )  > df1   c1 c2 1  a  1 2  b  2 3  c  3 4  d  4  > df2   c1 c2 1  c  3 2  d  4 3  e  5 4  f  6 

I need to perform set operation of these 2 data frames. I used merge(df1,df2,all=TRUE) and merge(df1,df2,all=FALSE) method to get the union and intersection of these data frames and got the required output. What is the function to get the minus of these data frames,that is all the positions existing on one data frame but not the other? I need the following output.

 c1 c2 1  a  1 2  b  2 

Answer 1

I remember coming across this exact issue quite a few months back. Managed to sift through my Evernote one-liners.

Note: This is not my solution. Credit goes to whoever wrote it (whom I can't seem to find at the moment).

If you don't worry about rownames then you can do:

df1[!duplicated(rbind(df2, df1))[-seq_len(nrow(df2))], ] #   c1 c2 # 1  a  1 # 2  b  2 

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Edit: A data.table solution:

dt1 <- data.table(df1, key="c1") dt2 <- data.table(df2) dt1[!dt2] 

or better one-liner (from v1.9.6+):

setDT(df1)[!df2, on="c1"] 

This returns all rows in df1 where df2$c1 doesn't have a match with df1$c1.