删除值频率小于 R 中的 x 的行

Question

I got a data frame in R like the following:

V1 V2 V3
1  2  3
1  43 54
2  34 53
3  34 51
3  43 42
...

And I want to delete all rows which value of V1 has a frequency lower then 2. So in my example the row with V1 = 2 should be deleted, because the value "2" only appears once in the column ("1" and "3" appear twice each).

I tired to add a extra column with the frequency of V1 in it to delete all rows where the frequency is > 1 but with the following I only get NAs in the extra column.

data$Frequency <- table(data$V1)[data$V1]

Thanks

Answer 1

You can try this:

library(dplyr)
df %>% group_by(V1) %>% filter(n() > 1)

Answer 2

You can also consider using data.table. We first count the occurence of each value in V1, then filter on those occurences being more than 1. Finally, we remove our count-column as we no longer need it.

library(data.table)

setDT(dat)
dat2 <- dat[,n:=.N,V1][n>1,,][,n:=NULL]

Or even quicker, thanks to RichardScriven:

dat[, .I[.N >= 2], by = V1]
> dat2
   V1 V2 V3
1:  1  2  3
2:  1 43 54
3:  3 34 51
4:  3 43 42

Answer 3

With this you do not need to load a library

res<-data.frame(V1=c(1,1,2,3,3,3),V2=rnorm(6),V3=rnorm(6))
res[res$V1%in%names(table(res$V1)>=2)[table(res$V1)>=2],]