R dtplyr summarise.dtplyr_step 將每組匯總為一行

# S3 method for dtplyr_step
summarise(.data, ..., .by = NULL, .groups = NULL)

library(dplyr, warn.conflicts = FALSE)

dt <- lazy_dt(mtcars)

dt %>%
  group_by(cyl) %>%
  summarise(vs = mean(vs))
#> Source: local data table [3 x 2]
#> Call:   `_DT38`[, .(vs = mean(vs)), keyby = .(cyl)]
#> 
#>     cyl    vs
#>   <dbl> <dbl>
#> 1     4 0.909
#> 2     6 0.571
#> 3     8 0    
#> 
#> # Use as.data.table()/as.data.frame()/as_tibble() to access results

dt %>%
  group_by(cyl) %>%
  summarise(across(disp:wt, mean))
#> Source: local data table [3 x 5]
#> Call:   `_DT38`[, .(disp = mean(disp), hp = mean(hp), drat = mean(drat), 
#>     wt = mean(wt)), keyby = .(cyl)]
#> 
#>     cyl  disp    hp  drat    wt
#>   <dbl> <dbl> <dbl> <dbl> <dbl>
#> 1     4  105.  82.6  4.07  2.29
#> 2     6  183. 122.   3.59  3.12
#> 3     8  353. 209.   3.23  4.00
#> 
#> # Use as.data.table()/as.data.frame()/as_tibble() to access results