Find duplicates in data table, calculate value

Welcome to the forum

we can match it to a group by case and sum up the members

Assign Activity:
dtResult = dtorig.Clone

Assign Activity:
dtResult =

(From d in dtOrig.AsEnumerable
Group d by k=d("ID").toString.Trim into grp=Group
Let sm = grp.Sum(Function (x) CInt(x("Value").toString.Trim))
Let ra = new Object(){k,sm}
Select r = dtResult.Rows.Add(ra)).CopyToDataTable