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()
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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