title: Count a value in a column in a data frame in R programming
body: <p>Hi my data looks like below:</p>
  
  <pre><code>Product Price Quantity Returns 
  Fridge  $260  20       3 
  Oven    $150  12       #N/A 
  Iron    $100  #N/A     5 
  Stove   $150  20       #N/A
  </code></pre>
  
  <p>I want R to return the number of times "#N/A" appears in the column Returns.</p>
  
  <p>Thanks for the help. I'm new to R and trying to self teach. </p>