HashMap problem

Hello all, after much dissapointment from a previous programming forum I hope I can get an answer from this one :) I'll try to be a specific as possible.

So I have some students which in this case will will be the Key and their mark which will be their Value.

This is my code so far.

Code:

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import java.util.*;
import java.io.IOException;

public class StudentMarks {
  public static void main(String[] args) throws IOException {
      Map<String, Integer> mp = new HashMap<String, Integer>();
      mp.put("Simon", 4);
      mp.put("Anna", 10);
      mp.put("Simon", 4);
      mp.put("Anna", 9);
      mp.put("Anna", 5);
      mp.put("Edward", 10);

      Iterator<String> i= mp.keySet().iterator();
      String k;

      while(i.hasNext()){
          k=i.next();
          System.out.println(k+"\t"+mp.get(k));
      }
  }
}

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The problem I'm having is this runs through the list and ignores duplicates, which it's meant to do but it still needs to count the mark just discard the name.

The output needs to be as follows

Merit order
Edward 1 10.0
Anna 3 8.0
Simon 2 4.0

So as you can see Edward as 1 mark with average of 10
Anna has 3 marks with average of 8
Simon has 2 marks with average of 4.

I just can't think what I need to change in that loop to make this happen. Any ideas? Would be much appreciated.

Please try not to type just one line if you could edit my actual code and type in bold what you have changed that would help me understand the code a lot more. Thanks again

Quote:

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Originally Posted by Java Junior

Hello all, after much dissapointment from a previous programming forum I hope I can get an answer from this one :) I'll try to be a specific as possible.

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Since this is a crospost, it's considered polite to include a link to that other post. We don't want to waste our time, or yours, repeating advice you've already received.

Quote:

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Originally Posted by Java Junior

The problem I'm having is this runs through the list and ignores duplicates, which it's meant to do but it still needs to count the mark just discard the name.

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So what do you want the map to hold? All of the grades? The average? The count? Both? Something else?

Quote:

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Originally Posted by Java Junior

Please try not to type just one line if you could edit my actual code and type in bold what you have changed that would help me understand the code a lot more. Thanks again

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That's not really how this works. This isn't a code service. We'll try to work through your problem with you, but don't count on somebody handing you code. You wouldn't really learn that way anyway.

That's just it I haven't received any help so I haven't had any advice for it to be repeated lol. I just want it to print it out in Merit order, so number of scores then next to it the average.

As you see with the Merit ordering below

Merit order
1 Edward 1 10.0 (Edward had 1 score and average of that score was 10)
2 Anna 3 8.0 (Anna had 3 scores and her average was 8)
3 Simon 2 4.0 (Simon had 2 scores and his average was 4)

Keeping all the individual scores for each person is enough to find the average and the number of scores; don't use a Map<String, Integer> but use a Map<String, List<Integer>> instead.
b.t.w. this is not so advanced ...

kind regards,

Jos

Quote:

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Originally Posted by JosAH

Keeping all the individual scores for each person is enough to find the average and the number of scores; don't use a Map<String, Integer> but use a Map<String, List<Integer>> instead.
b.t.w. this is not so advanced ...

kind regards,

Jos

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So if I just change that there's nothing more I need to change within the code? I'll try that in a bit thanks

Quote:

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Originally Posted by Java Junior

So if I just change that there's nothing more I need to change within the code? I'll try that in a bit thanks

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Well, you do have to add each individual score to that list ...

kind regards,

Jos

So for each student, you have to keep 2 values: mark count and mark sum (or average). So you need to create a class StudentInfo {count; sum;}
and HashMap<String, StudentInfo>, and the method

Code:

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put(String name, int grade) {
  info = new  StudentInfo() if was null;
  info.count++;
  info.sum+=grade;
}

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