title: how to concatenate multiple strings into one
body: <p>i am using <code>apply(&quot;,&quot;.join)</code> to concatenate,</p>
  <pre class="lang-none prettyprint-override"><code>ICPMMRM Charge_Code
  0000000646DE9C5 SHSD15
  0000000646DE9C5 6
  0000000646DE9C5 10
  </code></pre>
  <pre><code>network_report_A=network_ctct.groupby('ICPMMRM')['Charge_Code'].apply(str).apply(&quot;,&quot;.join)
  network_report_A.head()
  </code></pre>
  <pre class="lang-none prettyprint-override"><code>ICPMMRM
  0000000646DE9C5    0, , , , ,S,H,S,D,1,5,\n,1, , , , , , , , , ,6...
  0000000650DE2E7    3, , , , ,S,H,S,D,1,5,\n,4, , , , , , , , , ,6...
  0000002229DE6AA    6, , , , ,S,H,S,D,1,5,\n,7, , , , , , , , ,1,7...
  0000002464DED52    8, , , , , ,S,H,1,-,L,1,-,C,K,V,A,\n,9, , , , ...
  0000003723CEE85    1,6, , , , ,C,C,2,-,L,2,-,C,K,V,A,\n,1,7, , , ...
  Name: Charge_Code, dtype: object
  </code></pre>
  <p>but i expect the result like <code>SHSD15,6,10</code></p>