title: R can't drop NA columns , tried several approaches
body: <p>I have a column with dates. the file is exported from an excel format. </p>
  
  <pre><code>summary(u$date)
  
                   Min.               1st Qu.                Median                  Mean               3rd Qu.                  Max. 
  "2012-01-13 00:00:00" "2014-05-14 00:00:00" "2015-04-09 00:00:00" "2015-05-03 17:58:04" "2016-03-03 00:00:00" "2018-06-11 00:00:00" 
                   NA's 
                 "5748" 
  </code></pre>
  
  <p>I tried the following:</p>
  
  <pre><code>u%&gt;%drop_na(`date`)
  
  u&lt;-u[!is.na(u$`date`),]
  </code></pre>
  
  <p>Unfortunately it has no effect and the number of rows does not get smaller.
  Where am I going wrong ? </p>
  
  <p>i clearly want to drop the columns with NA</p>