title: Return column names based on condition
body: <p>I've a dataset with 18 columns from which I need to return the column names with the highest value(s) for each observation, simple example below. I came across <a href="https://stackoverflow.com/questions/42374599/r-return-column-name-based-on-conditions" title="this">this</a> answer, and it almost does what I need, but in some cases I need to combine the names (like <code>ab</code>in <code>maxcol</code>below). How should I do this?</p>
  
  <p>Any suggestions would be greatly appreciated! If it's possible it would be easier for me to understand a tidyverse based solution as I'm more familiar with that than base.</p>
  
  <p>Edit: I forgot to mention that some of the columns in my data have NAs.</p>
  
  <pre><code>library(dplyr, warn.conflicts = FALSE)
  
  #turn this
  Df &lt;- tibble(a = 4:2, b = 4:6, c = 3:5)
  
  #into this
  Df &lt;- tibble(a = 4:2, b = 4:6, c = 3:5, maxol = c("ab", "b", "b"))
  </code></pre>
  
  <p><sup>Created on 2018-10-30 by the <a href="https://reprex.tidyverse.org" rel="nofollow noreferrer">reprex package</a> (v0.2.1)</sup></p>