title: Pandas Groupby with Group Concat for integer values
body: <p>My pandas dataframe looks like this, I am looking to group it by keys and concatenate the id's comma separated and create a new dataframe. Now the issue here is id column is integer.</p>
  
  <pre><code>df:
            key      id
      0   abc     5073138
      1   abcd    5025923
      2   abc     7453197
      3   abcd    5032121
      4   abcd    5032121
      5   abc     5032121
  
  
  new df:
  
           key       id
       0  abc     5073138,7453197,5032121
       1  abcd    5025923,5096021,5032121
  </code></pre>
  
  <p>I tried using group by with apply and aggregate but didn't work</p>
  
  <pre><code>df.groupby('key').apply(lambda x: ','.join(x.id))
  
  df.groupby('key').agg({'id' : lambda x: ', '.join(str(x))})
  </code></pre>