How to get group-level statistics while preserving the original dataframe?

Question

I have the following dataframe

one <- c(\'one\',NA,NA,NA,NA,\'two\',NA,NA)
group1 <- c(\'A\',\'A\',\'A\',\'A\',\'B\',\'B\',\'B\',\'B\')
group2 <- c(\'C\         


        

Answer 1

library(dplyr)

df %>% group_by(group1, group2) %>% mutate(count = sum(!is.na(one)))

Source: local data frame [8 x 4]
Groups: group1, group2 [4]

     one group1 group2 count
     
1    one      A      C     1
2     NA      A      C     1
3     NA      A      C     1
4     NA      A      D     0
5     NA      B      E     1
6    two      B      E     1
7     NA      B      F     0
8     NA      B      F     0