title: Merging values of two columns of dataframe with different dtypes
body: <p>I have the following pandas <code>dataframe</code>:</p>
  
  <pre><code>import pandas as pd
  
  df = pd.DataFrame({"pos": [1, 2, 3], "chain": ["A", "B", "C"]})
  </code></pre>
  
  <p>Giving:</p>
  
  <pre><code>  chain  pos
  0     A    1
  1     B    2
  2     C    3
  </code></pre>
  
  <p>and <code>df.types</code>:</p>
  
  <pre><code>chain    object
  pos       int64
  dtype: object
  </code></pre>
  
  <p>I'm looking for a way to merge Series <code>df["chain"]</code> and <code>df["pos"]</code> to have the following:</p>
  
  <pre><code>   chain+pos
  0     A1
  1     B2
  2     C3
  </code></pre>
  
  <p>and <code>df.dtypes</code>:</p>
  
  <pre><code>chain+pos    object
  dtype: object
  </code></pre>
  
  <p>Is there an easy way to do it?</p>