>。将data.frame转换为data.table（ as.data.table（mtcars）），按cyl分组，我们得到总结的mpg，并将其转换为列表

We can use data.table. Convert the 'data.frame' to 'data.table' (as.data.table(mtcars)), grouped by 'cyl', we get the summary of 'mpg' and convert it to list

library(data.table)
as.data.table(mtcars)[, as.list(summary(mpg)), by = cyl]
#    cyl Min. 1st Qu. Median  Mean 3rd Qu. Max.
#1:   6 17.8   18.65   19.7 19.74   21.00 21.4
#2:   4 21.4   22.80   26.0 26.66   30.40 33.9
#3:   8 10.4   14.40   15.2 15.10   16.25 19.2

或仅使用 dplyr ，通过'cyl'分组后，我们使用 do 执行与上述相同的操作。

Or using only dplyr, after grouping by 'cyl', we use do to do the same operation as above.

library(dplyr)
mtcars %>%
     group_by(cyl) %>%
     do(data.frame(as.list(summary(.$mpg)), check.names=FALSE) )
#   cyl  Min. 1st Qu. Median  Mean 3rd Qu.  Max.
#  <dbl> <dbl>   <dbl>  <dbl> <dbl>   <dbl> <dbl>
#1     4  21.4   22.80   26.0 26.66   30.40  33.9
#2     6  17.8   18.65   19.7 19.74   21.00  21.4
#3     8  10.4   14.40   15.2 15.10   16.25  19.2

或使用 purrr

library(purrr)
mtcars %>% 
     slice_rows("cyl") %>% 
     select(mpg) %>%
     by_slice(dmap, summary, .collate= "cols")