r - How to write a function with same interface as dplyr::filter but which is doing something different -


i implement function has same interface filter method in dplyr instead of removing rows not matching condition would, instance, return array indicator variable, or attach such column returned tibble?

i find useful since allow me compute summaries of columns after , before filtering summaries of rows have been removed on single tibble.

i find dplyr::filter interface convenient , therefore emulate it.

i think group_by here

you might filter summarise so

library(dplyr) mtcars %>%   filter(cyl==4) %>%   summarise(mean=mean(gear))        # mean # 1 4.090909

you can group_by, summarise, filter

mtcars %>%   group_by(cyl) %>%   summarise(mean=mean(gear))   # optional filter here  # # tibble: 3 x 2     # cyl     mean   # <dbl>    <dbl> # 1     4 4.090909 # 2     6 3.857143 # 3     8 3.285714

you can group conditionals well, so

mtcars %>%   group_by(cyl > 4) %>%   summarise(mean=mean(gear))  # # tibble: 2 x 2   # `cyl > 4`     mean       # <lgl>    <dbl> # 1     false 4.090909 # 2      true 3.476190

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