mutate() now supports the argument .keep = "transmute"

[apalacio9502]

Hi @hadley and @DavisVaughan,

This merge request seeks to support the new .keep = "transmute" argument in the mutate, based on the dplyr pull request tidyverse/dplyr#7038

Below I leave an example comparing transmute with mutate(.keep = "transmute")

con <- DBI::dbConnect(RSQLite::SQLite(), ":memory:")

example <- tibble(
  group = c("a", "a", "b", "b"),
  old = c(1, 2, 3, 4)
)

example <- copy_to(con, example)

# transmute --------------------------------------------------------------------

example %>% transmute(
  group,
  new = old * 2,
  old
) %>% 
  show_query()

# <SQL>
SELECT `group`, `old` * 2.0 AS `new`, `old`
FROM `example`

# mutate(.keep = "transmute") --------------------------------------------------

example %>% mutate(
  .keep = "transmute",
  group,
  new = old * 2,
  old
) %>% 
  show_query()

# <SQL>
SELECT `group`, `old` * 2.0 AS `new`, `old`
FROM `example`

# group_by + transmute ---------------------------------------------------------

example %>% 
  group_by(group) %>% 
  transmute(
    new = sum(old,na.rm = TRUE),
    old
  ) %>% 
  ungroup() %>% 
  show_query()

# <SQL>
SELECT `group`, SUM(`old`) OVER (PARTITION BY `group`) AS `new`, `old`
FROM `example`

# group_by + mutate(.keep = "transmute") ---------------------------------------

example %>% 
  group_by(group) %>% 
  mutate(
    .keep = "transmute",
    new = sum(old,na.rm = TRUE),
    old
  ) %>% 
  ungroup() %>% 
  show_query()

# <SQL>
SELECT `group`, SUM(`old`) OVER (PARTITION BY `group`) AS `new`, `old`
FROM `example`

# mutate(.keep = "transmute", by = ...) ----------------------------------------

example %>%  
  mutate(
    .keep = "transmute",
    .by = "group",
    new = sum(old,na.rm = TRUE),
    old
  ) %>% 
  show_query()

# <SQL>
SELECT `group`, SUM(`old`) OVER (PARTITION BY `group`) AS `new`, `old`
FROM `example`

Regards,