dplyr: count unique values

Question

I have a data:

df <- data.frame(strain = 1:6, sample = c("a24", "a24", "a24", "a26", "a26", "a27"), region = c(rep("ny", 3), rep("detroit",3)))

I want to count the number of sample per region and get something like:

region	sample_count
ny	1
detroit	2

I.e. ny has only one sample "a24", and detroit has two samples "a26" and "a27"

Answer 1

this way:

library(dplyr)

df |> 
  group_by(region) |> 
  summarise(sample_count = n_distinct(sample))

Output is:

# A tibble: 2 × 2
  region  sample_count
  <chr>          <int>
1 detroit            2
2 ny                 1