title: Pandas - Join on multiple unique columns
body: <p>I have the following two dataframes:</p>
  
  <pre><code>   x_1  x_2      x_3    x_4        x_5  ID  x_count
  0  159  xyz  883nne2  28h93             10        1
  1  159  xyz  883nne2  28h93     lightz  10        2
  2  159  xyz  94mmm4k             heavy  15        2
  3  354  abc  94mmm4k                     3        1
  4  354  abc  94mmm4k   455h             15        1
  5  354  abc  94mmm4k             super   3        1
  6  354  abc  94mmm4k    53g             10        1
  </code></pre>
  
  <p>And:</p>
  
  <pre><code>   y_1  y_2      y_3    y_4     y_5  ID  y_count 
  0  159  xyz  883nne2  28h93          10       55
  1  159  xyz  883nne2  28h93  lightz  10       14
  2  159  xyz  94mmm4k          heavy  15       2
  3  354  abc  94mmm4k                  3       7
  </code></pre>
  
  <p>I am looking to join both tables and do math on the count columns, I am not sure what would be the best method to join these two tables. If you notice the x_1, x_2, x_3, x_4, x_5 columns have unique values that are being accounted for in the count column and each of their instances, the table with the y columns matches on some of the same unique instances found in the table with the x columns</p>
  
  <p>Here is what I was hoping the new dataframe would look like:</p>
  
  <pre><code>   x_1  x_2      x_3    x_4        x_5  ID  x_count y_1  y_2     y_3    y_4   y_5   ID  y_count
  0  159  xyz  883nne2  28h93             10        1 159  xyz  883nne2 28h93         10      55
  1  159  xyz  883nne2  28h93     lightz  10        2 159  xyz  883nne2 28h93  lightz 10      14
  2  159  xyz  94mmm4k             heavy  15        2 159  xyz  94mmm4k         heavy 15       2
  3  354  abc  94mmm4k                     3        1 354  abc  94mmm4k                3       7
  4  354  abc  94mmm4k   455h             15        1
  5  354  abc  94mmm4k             super   3        1
  6  354  abc  94mmm4k    53g             10        1
  </code></pre>
  
  <p>I've tried merging on the ID column and left join but it just duplicated these records and did give me the result shown above.</p>
  
  <p>Any guidance is greatly appreciated.</p>