Remove rows with same column value from DataTable and add corresponding values

Question

I have a DataTable with multiple columns. If the value of certain column repeats, I need to remove that row and add the quantities against it. For example, following datatable

ITEM    QTY
------------
1       20
2       10
2       10
3       20

would become:

ITEM    QTY
-----------
1       20
2       20
3       20

This is what I did

var table = dt.AsEnumerable() 
.GroupBy(row => row.Field("ITEM")) 
.Select(group => group.First()) 
.CopyToDataTable();

It removes the extra row but doesn't add up the quantities. So please help me in this regard.

Answer 1

You can use Sum. You just have to find the duplicate-rows first:

var dupGroups = dt.AsEnumerable()
    .GroupBy(row => row.Field<int>("ITEM"))
    .Where(g => g.Count() > 1);

Now you can use them to get the sum and to remove the redundant rows from the table.

foreach (var group in dupGroups)
{
    DataRow first = group.First();
    int sum = group.Sum(r => r.Field<int>("QTY"));
    first.SetField("QTY", sum);
    foreach (DataRow row in group.Skip(1))
        dt.Rows.Remove(row);
}

Or in one query which creates a new DataTable.

DataTable newTable = dt.AsEnumerable()
    .GroupBy(row => row.Field<int>("ITEM"))
    .Select(g => 
    {
        DataRow first = g.First();
        if (g.Count() > 1)
        {
            int sum = g.Sum(r => r.Field<int>("QTY"));
            first.SetField("QTY", sum);
        }
        return first;
    })
    .CopyToDataTable();

However, even the second approach modifies the original table which might be undesired since you use CopyToDatatable to create a new DataTable. You need to clone the original table(DataTable newTable = dt.Clone();) to get an empty table with the same schema. Then use NewRow + ItemArray.Clone() or table.ImportRow to create a real clone without modifying the original data.

See: C# simple way to copy or clone a DataRow?

Edit: Here is an example how you can create a clone without touching the original table:

DataTable newTable = dt.Clone();
var itemGroups = dt.AsEnumerable()
    .GroupBy(row => row.Field<int>("ITEM"));
foreach (var group in itemGroups)
{
    DataRow first = group.First();
    if (group.Count() == 1)
        newTable.ImportRow(first);
    else
    {
        DataRow clone = newTable.Rows.Add((object[])first.ItemArray.Clone());
        int qtySum = group.Sum(r => r.Field<int>("QTY"));
        clone.SetField("QTY", qtySum);
    }
}

Answer 2

var table = dt.AsEnumerable() 
    .GroupBy(row => row.Field<int>("ITEM")) 
    .Select(group => {
        var row = group.First();
        row['QTY'] = group.Sum(x => x.Field<int>('QTY'));
        return row;
    }).CopyToDataTable();

Answer 3

This won't change your original DataTable:

var table = dt.Copy().AsEnumerable()
                      .GroupBy(row=>row["ITEM"])
                      .Select(g=> {
                                DataRow dr = g.First();
                                dr.SetField("QTY", g.Sum(x=>x.Field<int>("QTY")));
                                return dr;
                             })
                      .CopyToDataTable();