Question

Below is the program I have for reading the .csv file and printing the output, but I am not able to achive the below functionality as mentioned in my input and output. I basically want to have the user ID listed separately if it’s avaialble in 2 different groups.

My input would be something like:

User ID       Group

ABC           Group1   
DEF           Group2
ABC           Group3
GHI           Group4

Since ABC is available in 2 different groups, I need the output as:

ABC     Group1
ABC     Group3

Can you please help?

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.FileWriter;
import java.util.StringTokenizer;

public class dumpRead {
    public static void main(String[] args) {
        try {

            //csv file containing data
            String strFile = "C:/Tracker/read/data.csv";

            //create BufferedReader to read csv file
            BufferedReader br = new BufferedReader( new FileReader(strFile));
            String strLine = "";
            StringTokenizer st = null;
            int lineNumber = 0, tokenNumber = 0;

            //read comma separated file line by line
            while( (strLine = br.readLine()) != null){
                lineNumber++;

                //break comma separated line using ","
                st = new StringTokenizer(strLine, ",");

                while(st.hasMoreTokens()){
                    //display csv values
                    tokenNumber++;
                    System.out.println("Token # " + tokenNumber 
                    + ", Token : "+ st.nextToken());
                }

                //reset token number
                tokenNumber = 0;                        
            }
        }
        catch(Exception e) {
            System.out.println("Exception while reading csv file: " +     e);                   
        }
    }
}

Answer 1

Parse all the user id’s and put it in a HashMap>

For each userid, check if it is already there in the hashmap, if it is already there, then get the corresponding Set and add it to the end of the list.
if hashmap does not contain the user, then create a new HashSet and add the group

Note: The idea behind HashSet, is it will ignore duplicates

The psuedo code will be something like this,

for(string user: users)
{
  if(hashmap.contains(user))
    {
       HashSet<Sting> usergroups = hashmap.get(user);
       usergroups.add(group);
    }
   else
    {
      HashSet<String> groups = new HashSet<String> ();
       groups.add(group);
    }
}