dplyr groups not working with dollar sign data$column syntax

user_16104842 0
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I'm looking to find the min and max values of a column for each group:

mtcars %>%
  group_by(mtcars$cyl) %>%
  summarize(
    min_mpg = min(mtcars$mpg),
    max_mpg = max(mtcars$mpg)
  )
# # A tibble: 3 x 3
#   `mtcars$cyl` min_mpg max_mpg
#          <dbl>   <dbl>   <dbl>
# 1            4    10.4    33.9
# 2            6    10.4    33.9
# 3            8    10.4    33.9

It works for the most part and the format of the dataset looks good. However, it gives the min and max of the entire dataset, not of each individual group.

summarize dplyr r-faq r group-by
1 Answers

Don't use $ inside dplyr functions, they expect unquoted column names.

mtcars$mpg is specifically referencing the whole column form the original input data frame, not the grouped the grouped tibble coming out of group_by. Change your code to remove the data$ and it will work:

mtcars %>%
  group_by(cyl) %>%
  summarize(
    min_mpg = min(mpg),
    max_mpg = max(mpg)
  )
# # A tibble: 3 x 3
#     cyl min_mpg max_mpg
#   <dbl>   <dbl>   <dbl>
# 1     4    21.4    33.9
# 2     6    17.8    21.4
# 3     8    10.4    19.2

(Not to mention it's a lot less typing!)

user_9030610
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