title: How can I extract all first value in a column from other column?
body: <p>I got a table like this:</p>
  <pre><code>house
  house
  house
  dog
  dog
  dog
  </code></pre>
  <p>And I would like to have only first occurrence of each different words. So I would like to have a column like this:</p>
  <pre><code>house     house
  house
  house
  dog       dog
  dog
  dog
  </code></pre>