title: How to interpret dplyr message `summarise()` regrouping output by 'x' (override with `.groups` argument)?
body: <p>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.</p>
  
  <p>Here is an example to recreate the output:</p>
  
  <pre><code>library(tidyverse)
  library(hablar)
  df &lt;- 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") %&gt;% 
    convert(chr(year,week)) %&gt;% 
    mutate(total_rodents = rowSums(select_if(., is.numeric))) %&gt;% 
    convert(num(year,week)) %&gt;% 
    group_by(year,week) %&gt;% summarise(average = mean(total_rodents))
  </code></pre>
  
  <p>The output tibble is correct, but this message appears:</p>
  
  <blockquote>
    <p><code>summarise()</code> regrouping output by 'year' (override with <code>.groups</code> argument)</p>
  </blockquote>
  
  <p>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? </p>
  
  <p>I don't think the message indicates a problem because it appears throughout the dplyr vignette:
  <a href="https://cran.r-project.org/web/packages/dplyr/vignettes/programming.html" rel="noreferrer">https://cran.r-project.org/web/packages/dplyr/vignettes/programming.html</a></p>
  
  <p>I believe it is a new message because it has only appeared on very recent SO questions such as <a href="https://stackoverflow.com/questions/62129863/how-to-use-pairwise-wilcox-test-using-dplyr">How to melt pairwise.wilcox.test output using dplyr?</a> and <a href="https://stackoverflow.com/questions/61973650/r-aggregate-over-multiple-columns/61974462#61974462">R Aggregate over multiple columns</a> (neither of which addresses the regrouping/override message). </p>
  
  <p>Thank you!</p>