从 DataTable 和自定义 IEqualityComparer中删除重复项

发布于 2024-08-08 08:13:13 字数 980 浏览 6 评论 0原文

我如何实现 IEqualityComparer以从具有下一个结构的 DataTable 中删除重复行：

ID primary key, col_1, col_2, col_3, col_4

默认比较器不起作用，因为每一行都有自己的、唯一的主行钥匙。

如何实现 IEqualityComparer 将跳过主键并仅比较剩余的数据。

我有这样的东西：

public class DataRowComparer : IEqualityComparer<DataRow>
{
 public bool Equals(DataRow x, DataRow y)
 {
  return
   x.ItemArray.Except(new object[] { x[x.Table.PrimaryKey[0].ColumnName] }) ==
   y.ItemArray.Except(new object[] { y[y.Table.PrimaryKey[0].ColumnName] });
 }

 public int GetHashCode(DataRow obj)
 {
  return obj.ToString().GetHashCode();
 }
}

但

public static DataTable RemoveDuplicates(this DataTable table)
{
  return
    (table.Rows.Count > 0) ?
  table.AsEnumerable().Distinct(new DataRowComparer()).CopyToDataTable() :
  table;
}

它只调用 GetHashCode() 而不会调用 Equals()

原文

How have I to implement IEqualityComparer<DataRow> to remove duplicates rows from a DataTable with next structure:

ID primary key, col_1, col_2, col_3, col_4

The default comparer doesn't work because each row has it's own, unique primary key.

How to implement IEqualityComparer<DataRow> that will skip primary key and compare only data remained.

I have something like this:

public class DataRowComparer : IEqualityComparer<DataRow>
{
 public bool Equals(DataRow x, DataRow y)
 {
  return
   x.ItemArray.Except(new object[] { x[x.Table.PrimaryKey[0].ColumnName] }) ==
   y.ItemArray.Except(new object[] { y[y.Table.PrimaryKey[0].ColumnName] });
 }

 public int GetHashCode(DataRow obj)
 {
  return obj.ToString().GetHashCode();
 }
}

and

public static DataTable RemoveDuplicates(this DataTable table)
{
  return
    (table.Rows.Count > 0) ?
  table.AsEnumerable().Distinct(new DataRowComparer()).CopyToDataTable() :
  table;
}

but it calls only GetHashCode() and doesn't call Equals()

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孤君无依 2024-08-15 08:13:14

这就是 Distinct 的工作方式。它本质上使用 GetHashCode 方法。您可以编写 GetHashCode 来执行您需要的操作。由于您更了解数据，因此

public int GetHashCode(DataRow obj)
{
    var values = obj.ItemArray.Except(new object[] { obj[obj.Table.PrimaryKey[0].ColumnName] });
    int hash = 0;
    foreach (var value in values)
    {
        hash = (hash * 397) ^ value.GetHashCode();
    }
    return hash;
}

您可能会想出更好的方法来生成哈希值。

That is the way Distinct works. Intenally it uses the GetHashCode method. You can write the GetHashCode to do what you need. Something like

public int GetHashCode(DataRow obj)
{
    var values = obj.ItemArray.Except(new object[] { obj[obj.Table.PrimaryKey[0].ColumnName] });
    int hash = 0;
    foreach (var value in values)
    {
        hash = (hash * 397) ^ value.GetHashCode();
    }
    return hash;
}

Since you know your data better you can probably come up with a better way to generate the hash.

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