Select rows with common ids in grouped data frame

Question

I am searching for a simpler solution to the following problem. Here is my setup:

test <- tibble::tribble(
  ~group_name, ~id_name, ~varA, ~varB,
     \"g         


        

Answer 1

In base R, we can split id_name by group_name find common id's and then subset

subset(test, id_name %in% Reduce(intersect, split(id_name, group_name)))

#   group_name id_name  varA varB 
#   <chr>      <chr>   <dbl> <chr>
# 1 groupA     id_1        1 a    
# 2 groupA     id_2        4 f    
# 3 groupA     id_4        6 x    
# 4 groupA     id_4        6 h    
# 5 groupB     id_1        2 s    
# 6 groupB     id_2       13 y    
# 7 groupB     id_4       14 t    
# 8 groupC     id_1        3 d    
# 9 groupC     id_2        7 j    
#10 groupC     id_4        9 l    

---

Using similar concept in tidyverse, it would be

library(tidyverse)
test %>%
  filter(id_name %in% (test %>%
                         group_split(group_name)  %>%
                         map(~pull(., id_name)) %>%
                         reduce(intersect)))

Answer 2

You can tabulate the the occurrence of id_name by group_name:

table(test$group_name,test$id_name)

If id_name is present in every group, we want columns that have all > 0 entris. We can simplify this logic using a combination of >0 and colMeans:

keep = names(which(colMeans(table(test$group_name,test$id_name)>0)==1))

Using this:

test[test$id_name %in% keep,]