No applicable method for 'anti_join' applied to an object of class "factor"

Question

I want to Identify the rows present in dataframe1 which are not present in dataframe2 based on a particular column. I have used the below code to get the desired information.

diffId <- anti_join(dat$ID,datwe$ID)

Unfortunately, I have encountered with an error:

Error in UseMethod("anti_join") :
no applicable method for 'anti_join' applied to an object of class "factor"

I have checked the class of the desired column in both the dataframes and which turned out to be factor. Have also tried to separate the column into a separate variable in an assumption that it might solve the issue, but of no luck !

fac1 <- datwe$ID
fac2 <- dat$ID
diffId <- anti_join(fac2,fac1)

Could you please share your thoughts ?

Thanks

Answer 1

Almost all dplyr functions operate on tbls (depending on the context it can be data.frame, data.table, database connection and so on) so what you really want is something like this:

> dat <- data.frame(ID=c(1, 3, 6, 4), x=runif(4))
> datwe <- data.frame(ID=c(3, 5, 8), y=runif(3))
> anti_join(dat, datwe, by='ID') %>% select(ID)
  ID
1  4
2  6
3  1

Note that ordering is clearly not preserved.

If you use factors (unlike numerics in the example above) with different levels there is a conversion between factor and character involved.

If you want to operate on vectors then you can use setdiff (available in both base and dplyr)

> setdiff(dat$ID, datwe$ID)
[1] 1 6 4