Dplyr: Count number of observations in group and summarise?

Question

Im wondering if there is a more elegant way to perform this.

Right now, I am grouping all observations by Species. Then I summarize the median values.

median <- iris %>% group_by(Species) %>% summarise(medianSL = median(Sepal.Length), medianSW = median(Sepal.Width), medianPL = median(Petal.Length), medianPW = median(Petal.Width))

I also wanted a column (n) that shows the amount of flowers in each row:

median_n <- iris %>% group_by(Species) %>% tally()

Can I combine these two code chunks? So that way the above code chunk will generate a table with the median lengths AND the total n for each row?

akrun · Accepted Answer · 2022-11-10 22:49:01Z

We may use across in summarise to loop over the numeric columns to get the median as well as create a frequency count with n() outside the across

library(dplyr) library(stringr) iris %>% group_by(Species) %>% summarise(across(where(is.numeric), ~ median(.x, na.rm = TRUE), .names = "median{str_remove_all(.col, '[a-z.]+')}"), n = n(), .groups = "drop")

-output

# A tibble: 3 × 6 Species medianSL medianSW medianPL medianPW n <fct> <dbl> <dbl> <dbl> <dbl> <int> 1 setosa 5 3.4 1.5 0.2 50 2 versicolor 5.9 2.8 4.35 1.3 50 3 virginica 6.5 3 5.55 2 50

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