How to find values shared between groups in a data frame? [duplicate]

Answer 1

Or you can group by val and then check whether the number of distinct exp for that val is equal to the data frame level number of distinct exp:

df %>% 
    group_by(val) %>% 
    mutate(shared = n_distinct(exp) == n_distinct(.$exp))
    # notice the first exp refers to exp for each group while .$exp refers 
    # to the overall exp column in the data frame

# A tibble: 12 x 3
# Groups:   val [6]
#   exp     val shared
#      
# 1 A        10 TRUE  
# 2 A        20 FALSE 
# 3 A        15 TRUE  
# 4 A        10 TRUE  
# 5 B        10 TRUE  
# 6 B        15 TRUE  
# 7 B        99 FALSE 
# 8 B         2 FALSE 
# 9 C        15 TRUE  
#10 C        20 FALSE 
#11 C        10 TRUE  
#12 C         4 FALSE