如何在R中使用purrr :: map（）

Question

Recently I got to know that the map function from purrr package is really powerful and tried to find out how to use it in the following case:

Using iris dataset and using purrr::map function, calculate max , mean , min for all variables Sepal.Length , Sepal.Width , Petal.Length , Petal.Width , respectively for each Species (setosa, versicolor, virginica). Then put the results into a list having

• a character: Species name, and
• four vectors: max , mean , min for Sepal.Length , Sepal.Width , Petal.Length , Petal.Width .

Any suggestions? I was using dplyr::mutate , but the result format is not what I want.

iris %>%
  group_by(Species) %>%
  summarise(MinSL=min(Sepal.Length),
            MaxSL=max(Sepal.Length),
            MeanSL=mean(Sepal.Length),
            MinPL=min(Petal.Length),
            MaxPL=max(Petal.Length),
            MeanPL=mean(Petal.Length))

It will be also nice see if there is a solution using dpylr to do the task. Thank you!

Answer 1

You don't need purrr. Try:

iris %>%
  group_by(Species) %>%
  summarise_at(vars(Sepal.Length, Sepal.Width, Petal.Length, Petal.Width),
               c("min", "max", "mean"))

Output

# A tibble: 3 x 13
  Species    Sepal.Length_min Sepal.Width_min Petal.Length_min Petal.Width_min
  <fct>                 <dbl>           <dbl>            <dbl>           <dbl>
1 setosa                 4.30            2.30             1.00           0.100
2 versicolor             4.90            2.00             3.00           1.00 
3 virginica              4.90            2.20             4.50           1.40 
# ... with 8 more variables: Sepal.Length_max <dbl>, Sepal.Width_max <dbl>,
#   Petal.Length_max <dbl>, Petal.Width_max <dbl>, Sepal.Length_mean <dbl>,
#   Sepal.Width_mean <dbl>, Petal.Length_mean <dbl>, Petal.Width_mean <dbl>