how to use arrange(x,.by_group=TRUE) if group_by() is not supported

[alejandrohagan]

Hi,

I love the package!

I know that group_by() is not supported when prudence level is set to 'stingy' however how can we do arrange within groups?

previously you could use group_bu() and then arrange(x,.by_group=TRUE).

Is there an alternative in duckplyr

[krlmlr]

Thanks. How is .by_group = TRUE different from prepending the grouping variables?

Request

data %>%
  group_by(a, b) %>%
  arrange(c, .by_group = TRUE)

Alternative

data %>%
  arrange(a, b, c)

[alejandrohagan]

hi -- sorry for delay.

The main issue is that you want to have defined order within group so that if you use some downstream functions like cummean or fill() it respects the groups order and boundary. The below examples give different outputs

library(tidyverse)

dat <- tibble(
  group=c(1,1,2,2,2,3,3,3)
  ,values=c(1,NA,NA,NA,2,1,4,2)
)



## intended solution
dat |> 
  group_by(group) |>
  arrange(desc(group),.by_group = TRUE) |> 
  fill(values,.direction="down")

## same values but table is flipped

dat |> 
  group_by(group) |>
  arrange(desc(group)) |> 
  fill(values,.direction="down") 

## wrong values
dat |> 
  arrange(desc(group)) |> 
  fill(values,.direction="down")

without group_by() how would we sort within groups and define group boundaries?