title: Finding values in a columns "a" which has different values in column "b" for two different data set
body: <p>Data contains multiple columns and 3000 row</p>
  
  <p>Same <code>OrderNo</code> but different <code>Ordertype</code>.</p>
  
  <p>I want to get all the <code>OrderNo</code> whose <code>Ordertype</code> are different in the two data frame. </p>
  
  <p>I have isolated the two columns from the two data frame and set them in ascending order. Then I tried to use the function <code>cbind</code> to combine the two columns and find the missing values in one of the columns. </p>
  
  <pre><code>xxx &lt;- data.frame( orderNo = c(1:10), Ordertype = c("a", "b", "c", "d", "a", "b", "c", "d", "e", "f"))
  yyy &lt;- data.frame( orderNo = c(1:10), Ordertype = c("a", "b", "c", "d", "a", "b", "e", "d", "e", "f"))
  </code></pre>
  
  <p>In the above example: <code>OrderNo</code> "7" corresponds to "c" in one data frame and "e" in another data frame. I want a set of all such number with a different value in the column <code>Ordertype</code> as my output.</p>