title: Delete rows with blank values in one particular column
body: <p>I am working on a large dataset, with some rows with NAs and others with blanks:</p>
  
  <pre><code>df &lt;- data.frame(ID = c(1:7),                                   
           home_pc = c("","CB4 2DT", "NE5 7TH", "BY5 8IB", "DH4 6PB","MP9 7GH","KN4 5GH"),               
           start_pc = c(NA,"Home", "FC5 7YH","Home", "CB3 5TH", "BV6 5PB",NA),               
           end_pc = c(NA,"CB5 4FG","Home","","Home","",NA))
  </code></pre>
  
  <p>How do I remove the NAs and blanks in one go (in the start_pc and end_pc columns)?  I have in the past used:</p>
  
  <pre><code>df&lt;- df[-which(is.na(df$start_pc)), ]
  </code></pre>
  
  <p>... to remove the NAs - is there a similar command to remove the blanks?</p>