title: Count NAs per row in dataframe
body: <p>I've got dataframe that has batch ID and the results of six tests performed on each batch. The data looks like this:</p>
  
  <pre><code>batch_id  test1  test2  test3  test4  test5  test6
  001       0.121     NA  0.340  0.877  0.417  0.662
  002       0.229  0.108     NA  0.638     NA  0.574
  </code></pre>
  
  <p>(there are a few hundred rows in this dataframe, only one row per batch_id)</p>
  
  <p>I'm looking for a way to count how many NAs there are for each batch_id (for each row). I feel like this should be do-able with a few lines of R code at the most, but I'm having trouble actually coding it.
  Any ideas?</p>