How to interpret dplyr message `summarise()` regrouping output by ‘x’ (override with `.groups` argument)?

by

I started getting a new message (see post title) when running group_by and summarise() after updating to dplyr development version 0.8.99.9003.

Here is an example to recreate the output:

library(tidyverse)
library(hablar)
df <- read_csv("year, week, rat_house_females, rat_house_males, mouse_wild_females, mouse_wild_males 
               2018,10,1,1,1,1
               2018,10,1,1,1,1
               2018,11,2,2,2,2
               2018,11,2,2,2,2
               2019,10,3,3,3,3
               2019,10,3,3,3,3
               2019,11,4,4,4,4
               2019,11,4,4,4,4") %>% 
  convert(chr(year,week)) %>% 
  mutate(total_rodents = rowSums(select_if(., is.numeric))) %>% 
  convert(num(year,week)) %>% 
  group_by(year,week) %>% summarise(average = mean(total_rodents))

The output tibble is correct, but this message appears:

summarise() regrouping output by ‘year’ (override with .groups argument)

How should this be interpreted? Why does it report regrouping only by ‘year’ when I grouped by both year and week? Also, what does it mean to override and why would I want to do that?

I don’t think the message indicates a problem because it appears throughout the dplyr vignette:
https://cran.r-project.org/web/packages/dplyr/vignettes/programming.html

I believe it is a new message because it has only appeared on very recent SO questions such as How to melt pairwise.wilcox.test output using dplyr? and R Aggregate over multiple columns (neither of which addresses the regrouping/override message).

Thank you!

5 Answers
5

Leave a Comment