title: Python Pandas If value in column B = equals [X, Y, Z] replace column A with "T"
body: <p>Say I have this array:</p>
  
  <pre><code>A, B
  1, G
  2, X
  3, F
  4, Z
  5, I
  </code></pre>
  
  <p>If column B equals [X, Y or Z] replace column A with value "T"</p>
  
  <p>I've found how to change values within the same column but not across, any help would be most appreciated.</p>