title: Reading the table data from Excel and displaying the number of unique combination of columns in Java
body: <p>Suppose I have an excel table as follows:
  <a href="https://i.stack.imgur.com/gQau6.png" rel="nofollow noreferrer">Sample Table</a></p>
  
  <p>Java program should read the table and compute the result as follows:</p>
  
  <p>No of Column2 type of C1: 2, they are 2 and 1</p>
  
  <p>No of Column3 type of C1: 2, they are 3 and 4</p>
  
  <p>No of Column4 type of C1: 1, that is 4</p>
  
  <p>I could read the excel file contents using Apache POI. Please let me know how to processes the data, Should I use Hashmap ? If possible plese help me with sample code.</p>