Summing multiple columns based upon unique value

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Grouping also can be done with more then 1 columns e.g.

From d in dtData.AsEnumerable
Group d by k1=d(…), k2=d(…) … into grp=Group
…

Also the Non-LINQ Approach of filtering the distinct values can be applied for more than 1 column.

Processing the group members can also be done for more then 1 columns

We would suggest rereading the provided link:
[HowTo] Overview on different options for grouping data and processing the groups

also, feel free to share sample data and a very clear and sharp formulated requirement description including the expected output description