score:0

Accepted answer
string newcolexpression = @"' ' + " + string.join(" + ",groupbycolumns) ; // prepend a space to ensure string concatenation
// e.g. "' ' + id1 + id2"

dt.columns.add("groupby",typeof(string),newcolexpression);

dt = dt.asenumerable()
       .groupby(r => r["groupby"])
       .select(g => g.orderby(r => r["pk"]).first())
       .copytodatatable();

dt.columns.remove("groupby");

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