title: Set cell value based on value in other cell
body: <p>I have a following table structure:</p>
  
  <pre><code>    --- c1 ------- c2 ---- c3 ------ c4
   r1: **0001**  **word1**
   r2:   0002      word2  **0001**  **word1**
   r3:   0003      word3    0002      word2
  </code></pre>
  
  <p>I would like to set column three values automatically, so that if there is some word in column 4, then program should check column 2 and try to find the same word. If found, then column 1 value should be used as a column 3 value.</p>
  
  <p>I could do that manually, but it's more work and it gets problematic if I ever add new rows. Column 1 value is equal to row number, so it's updated automatically if new rows added. Now I would like to set my data so that also column 3 would be updated automatically in those cases.</p>
  
  <p>What is the right formula to make that happen?</p>