How can I group a dataframe, then summarize a total number for each group, then divide by the number of items in that group?

Question

I used the Group_by function to give me the total sum of amounts by prod_cnt. But now I want to get the average amount per prod_cnt (average/prod_cnt) by prod_cnt group. When I try to divide by count = n(), it just returns (+) signs. How can I get this to work?

Answer 1

1. don't nest calls to summarize, just include a singgle call and multiple comma-delimited named arguments.
2. use n() instead of count=n().

Untested code:

library(dplyr)
HW_data_File %>%
  group_by(prod_cat) %>%
  summarize(
    Total_Sale = sum(amount),
    count = n(),
    Per_amount = sum(amount) / n()
  )

In order to not recalculate things (likely not a factor, but just for pedagogy), you can do:

HW_data_File %>%
  group_by(prod_cat) %>%
  summarize(
    Total_Sale = sum(amount),
    count = n()
  ) %>%
  mutate(
    Per_amount = Total_Sale / count
  )