title: how to remove NA in character vector in R
body: <p>How can I remove NAs in my dataset after ungrouping them in a character vector? </p>
  
  <p>this is the <strong>data set</strong> :</p>
  
  <pre><code>Mno     drugs
  
  100173  9
  100173  3
  100173   NA
  100173   NA
  100463  18
  100463  18
  100463  1
  100463   NA
  100463   NA
  100463   NA
  10061   18
  10061   9
  10061   2
  
  
  a &lt;- is.na(progression_diab)
  </code></pre>
  
  <p>I need the output like this:</p>
  
  <pre><code>s.no     Mno     drug3
  
  1       100173      9
  2       100173      3
  5       100463      18
  6       100463      18
  7       100463      1
  11      10061      18
  12      10061      9
  13      10061      2
  14      10061      3
  16      101793     0
  </code></pre>