如何在dplyr链中将数据框连接到自身？

Question

偶尔,我需要在dplyr链中将数据框加入到(通常是修改过的)版本中.像这样的东西:

df  <- data.frame(
     id = c(1,2,3)
   , status = c('foo','bar','meh')
   , spouseid = c(4,3,2)
)


df %>% 
  filter( status == 'foo' | status == 'bar') %>% 
  # join the filtered table to itself using the dot as the right-hand side
  left_join(., by = c('id' = 'spouseid'))

当我尝试的时候,我明白了Error in is.data.frame(y) : argument "y" is missing, with no default.

Answer 1

问题是使用点只是在左手边移动,所以上面写的方式只是将lhs传递进去left_join().要在左侧和右侧使用点,请使用点两次:

df %>% 
  filter( status == 'foo' | status == 'bar') %>% 
  # the first dot is x argument and the second dot is the y argument
  left_join(
      x = . 
    , y = . 
    , by = c('id' = 'spouseid')
  )

通过这种方式,你将lhs传递给两个参数,left_join()而不是像往常那样依赖于magrittr的隐式lhs.