Calculating average in QlikView

[#1]

I have two fields in my file - ID and Marks. I want to calculate average marks for each of the IDs present. For e.g., if my data is

ID           Marks

1               10

1               20

2               100

1               30

2               200    

2               300

3               50

2               400

My expression should return the following corresponding to each of the IDs:

ID         Avg Of Marks

1                  20

2                 250

3                  50

Can anyone help me on this?

[Gysbert_Wassenaar]

Create a straight table with ID as dimension and avg(Marks) as expression. See attached example.