title: pivot_wider does not seem to work with missing values. How to turn spread() into pivot_wider() when there is missing values
body: <p>as the spread() function is being replaced by the new pivot_wider() function, I was trying to use the pivot_wider() from now on but it does not seem to work because of the missing values. Any help is much appreciated</p>
  
  <pre><code># This is an example I saw on the web
  
  surveys &lt;- read.csv("http://kbroman.org/datacarp/portal_data_joined.csv",
                      stringsAsFactors = FALSE)
  library(dplyr)
  
  surveys %&gt;%
    filter(taxa == "Rodent",
           !is.na(weight)) %&gt;%
    group_by(sex,genus) %&gt;%
    summarize(mean_weight = mean(weight)) %&gt;% 
    spread(sex, mean_weight)```
  
  #It gives me the following output. This is what I would like to get
  # A tibble: 10 x 4
     genus              V1      F      M
     &lt;chr&gt;           &lt;dbl&gt;  &lt;dbl&gt;  &lt;dbl&gt;
   1 Baiomys          NA     9.16   7.36
   2 Chaetodipus      19.8  23.8   24.7 
   3 Dipodomys        81.4  55.2   56.2 
   4 Neotoma         168.  154.   166.  
   5 Onychomys        23.4  26.8   26.2 
   6 Perognathus       6     8.57   8.20
   7 Peromyscus       19.9  22.5   20.6 
   8 Reithrodontomys  11.1  11.2   10.2 
   9 Sigmodon         70.3  71.7   61.3 
  10 Spermophilus     NA    57    130  
  </code></pre>
  
  <pre><code>surveys %&gt;%
    filter(taxa == "Rodent",
           !is.na(weight)) %&gt;%
    group_by(sex,genus) %&gt;%
    summarize(mean_weight = mean(weight)) %&gt;%
    pivot_wider(
      names_from = sex,
      values_from = mean_weight,
      names_repair = "minimal"
      )
  
  It says the following
  Error: Column 1 must be named.
  Use .name_repair to specify repair.
  Run `rlang::last_error()` to see where the error occurred.
  </code></pre>