Obtain more variables after grouping, summarising with select (dplyr)

Question

My data frame:

date  | weekday | price
2018  | 1       | 25
2018  | 1       | 35
2019  | 2       | 40

I try to run this code under dplyr:

pi %>% 
  group_by(date) %>% 
  group_by(date) %>%
  summarise(price = sum(price, na.rm = T)) %>%
  select(price, date, weekday) %>%
  print()

It doesn't work.

Any solution? Thanks in advance

Answer 1

Follow the order: select-->group_by-->summarise

df%>%select(price, date, weekday)%>%
    group_by(date, weekday)%>%summarise(sum(price,na.rm=T))

Answer 2

People are correctly suggesting to group_by date and weekday, but if you have a lot of columns, that could be a pain to write out. Here's another idiom I frequently use for data.frames with lots of columns:

pi %>% 
  group_by(date) %>%
  mutate(price = sum(price, na.rm = T)) %>%
  filter(row_number() == 1)

This will keep all the first instances of each column variables without having to explicitly write them all out.