如何根据数据表[分组]并将结果放入另一个数据表中

您尝试过LINQ的Distinct（）函数吗？代码示例：

var groups = (
    from DataRow row in Process_dt.AsEnumerable()
    select new { 
        id = row.Field<Int16>("id"), 
        name = row.Field<string>("name") 
        }
    ).Distinct();

GroupBy将返回一个IGrouping集合，您可以通过以下方式进行迭代：

var dataTable = new DataTable();
dataTable.Columns.Add("id", typeof(Int16));
dataTable.Columns.Add("name_in", typeof(string));
foreach (var group in groups)
{
  dataTable.Rows.Add(group.Key, (group.First())["name_in"]);
}

您可以构建自己的CopyToDataTable，它接受任何类型的IEnumerable（不仅仅是DataRow）并返回一个新的DataTable:

var q=from row in Process_dt.AsEnumerable()
      group row by (int)row["id"] into IdGroup
      select new{id=IdGroup.Key,name=IdGroup.First()["name"]};
// following does not compile by default
// because input is not an IEnumerable<DataRow> but an anonymous type, you need code below
var tblResult = q.CopyToDataTable(); 

下面是一个实现（在MSDN的帮助下）：

public class ObjectShredder<T> {
    private System.Reflection.FieldInfo[] _fi;
    private System.Reflection.PropertyInfo[] _pi;
    private System.Collections.Generic.Dictionary<string, int> _ordinalMap;
    private System.Type _type;
    // ObjectShredder constructor.
    public ObjectShredder() {
        _type = typeof(T);
        _fi = _type.GetFields();
        _pi = _type.GetProperties();
        _ordinalMap = new Dictionary<string, int>();
    }
    /// <summary>
    /// Loads a DataTable from a sequence of objects.
    /// </summary>
    /// <param name="source">The sequence of objects to load into the DataTable.</param>
    /// <param name="table">The input table. The schema of the table must match that 
    /// the type T.  If the table is null, a new table is created with a schema 
    /// created from the public properties and fields of the type T.</param>
    /// <param name="options">Specifies how values from the source sequence will be applied to 
    /// existing rows in the table.</param>
    /// <returns>A DataTable created from the source sequence.</returns>
    public DataTable Shred(IEnumerable<T> source, DataTable table, LoadOption? options) {
        // Load the table from the scalar sequence if T is a primitive type.
        if (typeof(T).IsPrimitive) {
            return ShredPrimitive(source, table, options);
        }
        // Create a new table if the input table is null.
        if (table == null) {
            table = new DataTable(typeof(T).Name);
        }
        // Initialize the ordinal map and extend the table schema based on type T.
        table = ExtendTable(table, typeof(T));
        // Enumerate the source sequence and load the object values into rows.
        table.BeginLoadData();
        using (IEnumerator<T> e = source.GetEnumerator()) {
            while (e.MoveNext()) {
                if (options != null) {
                    table.LoadDataRow(ShredObject(table, e.Current), (LoadOption)options);
                } else {
                    table.LoadDataRow(ShredObject(table, e.Current), true);
                }
            }
        }
        table.EndLoadData();
        // Return the table.
        return table;
    }
    public DataTable ShredPrimitive(IEnumerable<T> source, DataTable table, LoadOption? options) {
        // Create a new table if the input table is null.
        if (table == null) {
            table = new DataTable(typeof(T).Name);
        }
        if (!table.Columns.Contains("Value")) {
            table.Columns.Add("Value", typeof(T));
        }
        // Enumerate the source sequence and load the scalar values into rows.
        table.BeginLoadData();
        using (IEnumerator<T> e = source.GetEnumerator()) {
            Object[] values = new object[table.Columns.Count];
            while (e.MoveNext()) {
                values[table.Columns["Value"].Ordinal] = e.Current;
                if (options != null) {
                    table.LoadDataRow(values, (LoadOption)options);
                } else {
                    table.LoadDataRow(values, true);
                }
            }
        }
        table.EndLoadData();
        // Return the table.
        return table;
    }
    public object[] ShredObject(DataTable table, T instance) {
        FieldInfo[] fi = _fi;
        PropertyInfo[] pi = _pi;
        if (instance.GetType() != typeof(T)) {
            // If the instance is derived from T, extend the table schema
            // and get the properties and fields.
            ExtendTable(table, instance.GetType());
            fi = instance.GetType().GetFields();
            pi = instance.GetType().GetProperties();
        }
        // Add the property and field values of the instance to an array.
        Object[] values = new object[table.Columns.Count];
        foreach (FieldInfo f in fi) {
            values[_ordinalMap[f.Name]] = f.GetValue(instance);
        }
        foreach (PropertyInfo p in pi) {
            values[_ordinalMap[p.Name]] = p.GetValue(instance, null);
        }
        // Return the property and field values of the instance.
        return values;
    }
    public DataTable ExtendTable(DataTable table, Type type) {
        // Extend the table schema if the input table was null or if the value 
        // in the sequence is derived from type T.            
        foreach (FieldInfo f in type.GetFields()) {
            if (!_ordinalMap.ContainsKey(f.Name)) {
                // Add the field as a column in the table if it doesn't exist
                // already.
                DataColumn dc = table.Columns.Contains(f.Name) ? table.Columns[f.Name]
                    : table.Columns.Add(f.Name, f.FieldType);
                // Add the field to the ordinal map.
                _ordinalMap.Add(f.Name, dc.Ordinal);
            }
        }
        foreach (PropertyInfo p in type.GetProperties()) {
            if (!_ordinalMap.ContainsKey(p.Name)) {
                // Add the property as a column in the table if it doesn't exist
                // already.
                DataColumn dc = table.Columns.Contains(p.Name) ? table.Columns[p.Name]
                    : table.Columns.Add(p.Name, p.PropertyType);
                // Add the property to the ordinal map.
                _ordinalMap.Add(p.Name, dc.Ordinal);
            }
        }
        // Return the table.
        return table;
    }
}

现在你可以添加这些扩展：

public static class CustomLINQtoDataSetMethods {
    public static DataTable CopyToDataTable<T>(this IEnumerable<T> source) {
        return new ObjectShredder<T>().Shred(source, null, null);
    }
    public static DataTable CopyToDataTable<T>(this IEnumerable<T> source,
                                                DataTable table, LoadOption? options) {
        return new ObjectShredder<T>().Shred(source, table, options);
    }
}

瞧！现在CopyToDataTable可以处理任何LINQ查询：）