group by and filter data management using dplyr

Question

Take a simple dataset

a <- c(1,2,3,4,5,6,7,8)
b <- c(1,2,2,1,2,2,2,2)
c <- c(1,1,1,2,2,2,3,3)
d <- data.frame(a,b,c)

now I want

Answer 1

You can try

df <- d %>% mutate(test = ifelse((b != 1) == T, 0, 1)) %>% group_by(c) %>% 
            mutate(test = sum(test)) %>% filter(test != 0) %>% select(-test)

which yields

#  a b c
#1 1 1 1
#2 2 2 1
#3 3 2 1
#4 4 1 2
#5 5 2 2
#6 6 2 2