合并内存中的两个数据表并将它们分组以获取列的总和.使用linq，但在这里有点迷路

您希望使用完全外部联接的实现。如下所示。

一些设置，因此您可以自己尝试：

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);

查询如下所示：

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"]
            };

解决了这个问题

table1.Merge(table2, true, MissingSchemaAction.Add);
finalTable = table1.Clone();
finalTable.PrimaryKey = new DataColumn[] { finalTable.Columns["ID"], finalTable.Columns["Name"] };
List<string> columnNames = new List<string>();
for (int colIndex = 2; colIndex < finalTable.Columns.Count; colIndex++)
{
columnNames.Add(finalTable.Columns[colIndex].ColumnName);
}
foreach (string cols in columnNames)
{
var temTable = new DataTable();
temTable.Columns.Add("ID", typeof(int));
temTable.Columns.Add("Name", typeof(string));
temTable.Columns.Add(cols, typeof(decimal));
(from row in table1.AsEnumerable()
group row by new { ID = row.Field<int>("ID"), Team = row.Field<string>("Team") } into grp
orderby grp.Key.ID
select new
{
ID = grp.Key.ID,
Name = grp.Key.Team,
cols = grp.Sum(r =>  r.Field<decimal?>(cols)),
})
.Aggregate(temTable, (dt, r) => { dt.Rows.Add(r.ID, r.Team, r.cols); return dt; });
finalTable.Merge(temTable, false, MissingSchemaAction.Ignore);
}

由于列是动态的，因此您需要返回具有动态属性的对象。你可以用一个 ExpandoObject 来做到这一点。

下面的代码在很多方面都很丑陋 - 我会在放手之前做一些大规模的重构 - 但它可以完成工作，并可能帮助你实现你想要的。
(很抱歉使用了其他 linq 语法。

var query = table1.AsEnumerable()
    .GroupBy(row => new
                    {
                        ID = row.Field<int>("ID"),
                        Name = row.Field<string>("Name")
                    })
    .Select(grp =>
    {
        dynamic result = new ExpandoObject();
        var dict = result as IDictionary<string, object>;
        result.ID = grp.Key.ID;
        result.Name = grp.Key.Name;
        foreach (DataRow row in grp)
        {
            foreach (DataColumn column in table1.Columns)
            {
                string columnName = column.ColumnName;
                if (columnName.Equals("ID") || columnName.Equals("Name"))
                    continue;
                //else
                if (!dict.Keys.Contains(columnName))
                    dict[columnName] = row[columnName];
                else
                {
                    if (row[columnName] is System.DBNull)
                        continue;
                    if (dict[columnName] is System.DBNull)
                    {
                        dict[columnName] = row[columnName];
                        continue;
                    }
                    //else
                    dict[columnName] = (decimal)dict[columnName] + (decimal)row[columnName];
                }
            }
        }
        return result;
    });