title: Change a pandas DataFrame column value based on another column value
body: <p>I have a dataframe with two columns each of which represents an organism. They are called ORG1  and ORG2
  I want to move the values of ORG2 into ORG1 for the corresponding index value.</p>
  
  <p>So, if ORG1 is 'A' and ORG2 is 'B' I want ORG1 to take the value 'B' from ORG2.</p>
  
  <p>I have already started work to identify indexes of the ORG2 organisms that I want to move, as follows:</p>
  
  <pre><code>def move_org2(x):
      org2_matches = Series(x.ORG2.str.count("ESBL"))
      return x.ix[org2_matches == 1]
  
  org2_DF = move_org2(DF)
  
  org2_DF.ORG2.index
  </code></pre>
  
  <p>What is the best way to use this to change ORG1 values with the values at corresponding ORG2 indices</p>