title: How to form tuple column from two columns in Pandas
body: <p>I've got a Pandas DataFrame and I want to combine the 'lat' and 'long' columns to form a tuple.</p>
  
  <pre><code>&lt;class 'pandas.core.frame.DataFrame'&gt;
  Int64Index: 205482 entries, 0 to 209018
  Data columns:
  Month           205482  non-null values
  Reported by     205482  non-null values
  Falls within    205482  non-null values
  Easting         205482  non-null values
  Northing        205482  non-null values
  Location        205482  non-null values
  Crime type      205482  non-null values
  long            205482  non-null values
  lat             205482  non-null values
  dtypes: float64(4), object(5)
  </code></pre>
  
  <p>The code I tried to use was:</p>
  
  <pre><code>def merge_two_cols(series): 
      return (series['lat'], series['long'])
  
  sample['lat_long'] = sample.apply(merge_two_cols, axis=1)
  </code></pre>
  
  <p>However, this returned the following error:</p>
  
  <pre><code>---------------------------------------------------------------------------
   AssertionError                            Traceback (most recent call last)
  &lt;ipython-input-261-e752e52a96e6&gt; in &lt;module&gt;()
        2     return (series['lat'], series['long'])
        3 
  ----&gt; 4 sample['lat_long'] = sample.apply(merge_two_cols, axis=1)
        5
  </code></pre>
  
  <p>...</p>
  
  <pre><code>AssertionError: Block shape incompatible with manager 
  </code></pre>
  
  <p>How can I solve this problem?</p>