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    <p>You want to use an implementation of a full outer join. Something like what follows.</p> <p>Some setup so you can try this yourself:</p> <pre><code>DataTable t1 = new DataTable(); t1.Columns.Add("ID", typeof(int)); t1.Columns.Add("Name", typeof(string)); t1.Columns.Add("P1", typeof(double)); t1.Columns.Add("P2", typeof(double)); t1.Columns.Add("P3", typeof(double)); DataRow dr1 = t1.NewRow(); dr1["ID"] = 1; dr1["Name"] = "A1"; dr1["P1"] = 1; dr1["P2"] = 2; dr1["P3"] = 3.3; t1.Rows.Add(dr1); DataRow dr2 = t1.NewRow(); dr2["ID"] = 2; dr2["Name"] = "A2"; dr2["P1"] = 4.4; dr2["P2"] = 5; dr2["P3"] = 6; t1.Rows.Add(dr2); DataTable t2 = new DataTable(); t2.Columns.Add("ID", typeof(int)); t2.Columns.Add("Name", typeof(string)); t2.Columns.Add("P1", typeof(double)); t2.Columns.Add("P2", typeof(double)); t2.Columns.Add("P4", typeof(double)); DataRow dr3 = t2.NewRow(); dr3["ID"] = 1; dr3["Name"] = "A1"; dr3["P1"] = 10; dr3["P2"] = 11; dr3["P4"] = 12; t2.Rows.Add(dr3); DataRow dr4 = t2.NewRow(); dr4["ID"] = 2; dr4["Name"] = "A2"; dr4["P1"] = 12; dr4["P2"] = 14; dr4["P4"] = 15; t2.Rows.Add(dr4); DataRow dr5 = t2.NewRow(); dr5["ID"] = 3; dr5["Name"] = "A3"; dr5["P1"] = 16; dr5["P2"] = 17; dr5["P4"] = 18; t2.Rows.Add(dr5); </code></pre> <p>The queries look like:</p> <pre><code>var ids = (from r1 in t1.AsEnumerable() select new { ID = r1["ID"], Name = r1["Name"] }).Union( from r2 in t2.AsEnumerable() select new { ID = r2["ID"], Name = r2["Name"] }); var query = from id in ids join r1 in t1.AsEnumerable() on id equals new { ID = r1["ID"], Name = r1["Name"] } into left from r1 in left.DefaultIfEmpty() join r2 in t2.AsEnumerable() on id equals new { ID = r2["ID"], Name = r2["Name"] } into right from r2 in right.DefaultIfEmpty() select new { ID = (r1 == null) ? r2["ID"] : r1["ID"], Name = (r1 == null) ? r2["Name"] : r1["Name"], P1 = (r1 == null) ? r2["P1"] : (r2["P1"] == null) ? r1["P1"] : (double)r1["P1"] + (double)r2["P1"], P2 = (r1 == null) ? r2["P2"] : (r2["P2"] == null) ? r1["P2"] : (double)r1["P2"] + (double)r2["P2"], P3 = (r1 == null) ? null : r1["P3"], P4 = (r2 == null) ? null : r2["P4"] }; </code></pre>
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    1. POMerging two datatable in memory and grouping them to get sum of columns.Using linq but kind of lost here
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    1. USFlyingStreudel
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