Calculate relative frequency for a certain group

Question

I have a data.frame of categorical variables that I have divided into groups and I got the counts for each group.

My original data nyD looks like:

Source: local         


        

Answer 1

You can do this whole thing in one step (from your original data nyD and without creating ny1). That is because when you'll run mutate after summarise, dplyr will drop one aggregation level (v2) by default (certainly my favorite feature in dplyr) and will aggregate only by v1

nyD %>% 
   group_by(v1, v2) %>%
   summarise(count = n()) %>%
   mutate(prop = count/sum(count))

# Source: local data frame [5 x 4]
# Groups: v1
# 
#   v1    v2 count      prop
# 1  a minus     1 0.3333333
# 2  a  plus     2 0.6666667
# 3  b minus     1 0.5000000
# 4  b     x     1 0.5000000
# 5  c     x     2 1.0000000

Or a shorter version using count (Thanks to @beginneR)

df %>% 
  count(v1, v2) %>% 
  mutate(prop = n/sum(n))