title: filtering rows based on multiple conditions
body: <p>With the following dataframe, I would like to filter out rows based on two conditions. If the daily temperature is less than 41 I would like to extract the epi temperature, if it is &gt;= 41 I would like to extract the meta temperature.</p>
  <pre><code>df &lt;- data.frame(day = c(1, 1, 1, 2, 2, 2),
             temperature = c(40, 39, 39, 45, 38, 30),
             strata = c(&quot;epi&quot;, &quot;meta&quot;, &quot;hypo&quot;, &quot;epi&quot;, &quot;meta&quot;, &quot;hypo&quot;))
  </code></pre>
  <p>desired output:</p>
  <pre><code>day temperature strata
  1    40         epi
  2    38         meta
  
  </code></pre>
  <p>I cant quite wrap my head around how to code this using tidyverse.</p>