比较数据表并将不匹配的行保存在第三个数据表中

Question

我正在尝试比较两个数据表并捕获第三个数据表中的差异。

DataTable one = new DataTable();
one.Columns.Add("ID");
one.Columns.Add("PCT");
one.Rows.Add("1", "0.1");
one.Rows.Add("2", "0.2");
one.Rows.Add("3", "0.3");
DataTable two = new DataTable();
two.Columns.Add("ID");
two.Columns.Add("PCT");
two.Columns.Add("OldPCT");
two.Rows.Add("1", "0.1", "0");
two.Rows.Add("2", "0.1", "0");
two.Rows.Add("3", "0.9", "0");
two.Columns.Remove("OldPCT");

//First method
DataTable three = two.AsEnumerable().Except(one.AsEnumerable()).CopyToDataTable();
foreach (DataRow dr in three.AsEnumerable())
{
    string strID = dr[0].ToString();
    string strPCT = dr[1].ToString();
}

//second method
var diffName = two.AsEnumerable().Select(r => r.Field<string>("PCT")).Except(one.AsEnumerable().Select(r => r.Field<string>("PCT")));
if (diffName.Any())
{
    DataTable Table3 = (from row in two.AsEnumerable()
                        join name in diffName
                        on row.Field<string>("PCT") equals name
                        select row).CopyToDataTable();
}

到目前为止，我已经尝试了两种方法，但没有得到预期的结果，应该是这样的。

在第三个数据表中，值应如下所述。

 ID    PCT
 2     O.1
 3     0.9   

最近的一个：

DataTable one = new DataTable();
one.Columns.Add("ID");
one.Columns.Add("PCT");
one.Rows.Add("1", "0.1");
one.Rows.Add("2", "0.2");
one.Rows.Add("2", "0.2");
one.Rows.Add("3", "0.3");
one.Rows.Add("3", "0.3");
DataTable two = new DataTable();
two.Columns.Add("ID");
two.Columns.Add("PCT");
two.Rows.Add("1", "0.1");
two.Rows.Add("2", "0.1");
two.Rows.Add("2", "0.1");
two.Rows.Add("3", "0.8");
two.Rows.Add("3", "0.9");

现在我需要从数据表 2 中获取除第一行之外的所有行。但我只得到最后三行。

Answer 1

你需要一个自定义的 IEqualityComparer

void Main()
{
   DataTable one = new DataTable();
   one.Columns.Add("ID");
   one.Columns.Add("PCT");
   one.Rows.Add("1", "0.1");
   one.Rows.Add("2", "0.2");
   one.Rows.Add("3", "0.3");
   DataTable two = new DataTable();
   two.Columns.Add("ID");
   two.Columns.Add("PCT");
   two.Columns.Add("OldPCT");
   two.Rows.Add("1", "0.1", "0");
   two.Rows.Add("2", "0.1", "0");
   two.Rows.Add("3", "0.9", "0");
   two.Columns.Remove("OldP

   DataTable three = two.AsEnumerable().Except(one.AsEnumerable(),new RowEqualityComparer()).CopyToDataTable();
   foreach (DataRow dr in three.AsEnumerable())
   {
       string strID = dr[0].ToString();
       string strPCT = dr[1].ToString();
   }
}


class RowEqualityComparer : IEqualityComparer<DataRow>
{
   public bool Equals(DataRow b1, DataRow b2)
   {
     if ((b1.Field<string>("ID") == b2.Field<string>("ID")) && (b1.Field<string>("PCT") == b2.Field<string>("PCT")))
     {
       return true;
     }
     else
     {
       return false;
     }
   }

   public int GetHashCode(DataRow bx)
   {
     return (bx.Field<string>("ID")+bx.Field<string>("PCT")).GetHashCode();
   }
}

Answer 2

基于 Hogan 的回答，您可以使用 DataRowComparer.Default 作为 Except() 方法的第二个参数（而不是创建自定义 IEqualityComparer）：

// this will get all rows from table two that don't match rows in one
// the result is an IEnumerable<DataRow> 
var unmatched = two.AsEnumerable()
  .Except(one.AsEnumerable(), DataRowComparer.Default);

// CopyToDataTable converts an IEnumerable<DataRow> into a DataTable
// but it blows up if the source object is empty

// this statement makes sure unmatched has data before calling CopyToDataTable()
// if it is empty, we 'clone' (make an empty copy) of one of the original DataTables
var three = unmatched.Any() ? unmatched.CopyToDataTable() : one.Clone();

这将对每行中的字段进行基于值的比较，以确定它们是否相等。