title: python pandas - replace number with string
body: <p>I have a DataFrame as;</p>
  
  <pre><code>data = pd.DataFrame({
         'A': [1,1,1,-1,1,1],
         'B':['abc','def','ghi','jkl','mno','pqr']
         })
  
  data['A'].replace(1,2)
  </code></pre>
  
  <p>returns;</p>
  
  <pre><code>0    2
  1    2
  2    2
  3   -1
  4    2
  5    2
  </code></pre>
  
  <p>But why doesn't <code>data['A'].replace(1,"pos")</code> work?</p>