title: Python Pandas merge if numbers equal
body: <p>Im trying to merge two csv's based on a condition.  The Value 'KEYS' on csv2 has to match the 'TCNUM' on CSV1, and append it the third column.  The csv's are very large and it has to be done through code.</p>
  
  <p>df1 - CSV1:</p>
  
  <pre><code>ID                                       TC_NUM
  dialog_testcase_0101.0001_greeting.xml  101.0001
  dialog_testcase_0101.0002_greeting.xml  101.0002
  dialog_testcase_0101.0003_greeting.xml  101.0003
  dialog_testcase_0101.0004_greeting.xml  101.0004
  dialog_testcase_0101.0005_greeting.xml  101.0005
  dialog_testcase_0101.0006_greeting.xml  101.0006
  dialog_testcase_0901.0008_greeting.xml  901.0007
  dialog_testcase_0101.0008_greeting.xml  101.0008
  dialog_testcase_0501.001_greeting.xml   501.001
  dialog_testcase_0801.0011_greeting.xml  801.0011
  </code></pre>
  
  <p>df2 - CSV2: </p>
  
  <pre><code>KEYS             TC_NUM
  FIT-3982    TC 101.0011, 101.0004
  FIT-3980    TC 801.0011.901.007
  FIT-3979    TC 101.0006, 501.001, 1907.0019, 1907.0020, 1907.0021
  </code></pre>
  
  <p>What I want:</p>
  
  <p>csvFinal:</p>
  
  <pre><code>ID                                       TC_NUM        Keys
  dialog_testcase_0101.0001_greeting.xml  101.0011     FIT-3982  
  dialog_testcase_0101.0002_greeting.xml  101.0002       
  dialog_testcase_0101.0003_greeting.xml  101.0006     FIT_3979
  dialog_testcase_0101.0004_greeting.xml  101.0004     FIT-3982
  dialog_testcase_0101.0005_greeting.xml  101.0005
  dialog_testcase_0101.0006_greeting.xml  101.0011     FIT_3982
  dialog_testcase_0901.0008_greeting.xml  901.0007     FIT_3979
  dialog_testcase_0101.0008_greeting.xml  101.0008
  dialog_testcase_0501.001_greeting.xml   501.001      FIT-3979
  dialog_testcase_0801.0011_greeting.xml  801.0011     FIT-3980
  </code></pre>
  
  <p>My code ..</p>
  
  <pre><code>mergedOpen = pd.merge(df1, df2, on=['TC_NUM'])
  mergedOpen.set_index('TC_NUM', inplace=True)
  
  mergedOpen.to_csv('MergedCSVOPEN.csv')
  </code></pre>