how to find average of each column of a datatable using c# - linq

Question

I have a .csv file containing names, roll, subjects correspondingly.I parsed it into a datatable and I calculated the highest mark of each subject. All i want to calculate is the average of each Subject. Can anyone help me with this !!!!!
This was my output.
Highest mark for ComputerScience:
Name : Manoj
Roll Number : 1212334556
Mark : 94
Highest Mark for Biology:
Name : Sandeep
Roll Number : 1223456477
Mark : 90
Highest Mark for Commerce:
Name : BarathRam
Roll Number : 1212345664
Mark : 97
And csv file contains Names,Rollno, Computer, Biology, Commerce.
Now all i need to get is the average of each subject
My code:
static DataTable table;
static void Main(string[] args)
{
StreamReader r = new StreamReader(#"C:\Users\GOPINATH\Desktop\stud1.csv");
string line = r.ReadLine(); //reads first line - column header
string[] part = line.Split(','); //splits the line by comma
createDataTable(part);
//copy from CSV to DataTable<String,String,int,int,int>
while ((line = r.ReadLine()) != null)
{
try
{
part = line.Split(',');
table.Rows.Add(part[0], part[1], Convert.ToInt32(part[2]), Convert.ToInt32(part[3]), Convert.ToInt32(part[4]));
}
catch(Exception e)
{
Console.WriteLine(e.Message);
}
}
r.Close();
int mark1_index = 0, mark2_index = 0, mark3_index = 0; //initailize index value 0 for highest marks
//finding the index of the highest mark for each subject
for(int i=0 ; i<table.Rows.Count ; i++)
{
if (Convert.ToInt32(table.Rows[i][2]) > Convert.ToInt32(table.Rows[mark1_index][2])) //subject1
{
mark1_index = i;
}
if (Convert.ToInt32(table.Rows[i][3]) > Convert.ToInt32(table.Rows[mark2_index][3])) //subject2
{
mark2_index = i;
}
if (Convert.ToInt32(table.Rows[i][4]) > Convert.ToInt32(table.Rows[mark3_index][4])) //subject3
{
mark3_index = i;
}
}
printmark(table,mark1_index, 2);
printmark(table,mark2_index, 3);
printmark(table,mark3_index, 4);
Console.Read();
}
public static void createDataTable(string[] columnName)
{
//create DataTable<String,String,int,int,int>
table = new DataTable();
table.Columns.Add(columnName[0], typeof(String));
table.Columns.Add(columnName[1], typeof(String));
table.Columns.Add(columnName[2], typeof(int));
table.Columns.Add(columnName[3], typeof(int));
table.Columns.Add(columnName[4], typeof(int));
}
public static void printmark(DataTable t, int rowIndex, int columnIndex)
{
Console.WriteLine("Highest mark for " + t.Columns[columnIndex].ColumnName + ":");
Console.WriteLine("\tName: " + (string)t.Rows[rowIndex][0]);
Console.WriteLine("\tRole Number: " + (string)t.Rows[rowIndex][1]);
Console.WriteLine("\tMark: " + (int)t.Rows[rowIndex][columnIndex]);
}
}
}

Answer 1

You could use Linq and do this.
DataTable t;
var average = t.AsEnumerable().Average(x=> x.Field<int>("columnname"));

Answer 2

var result=table.AsEnumerable()
.GroupBy(x=>x.Field<string>("Subject"))
.Select(x=>new
{
Subject=x.Key,
Average=x.Average(x=> x.Field<int>("Mark"));
}).ToList();
In order to calculate the average mark by Subject, first you need to groupby Subject then calculate the average for each group.