How to: Select distinct values from Dataset

Dataset is a most powerful and easy-to-use component of ADO.Net. In this section you will see how to get the distinct values from the Dataset.

CODE:

#region DATASET HELPER

private bool ColumnEqual(object A, object B)

{

    // Compares two values to see if they are equal. Also compares DBNULL.Value.           

    if (A == DBNull.Value && B == DBNull.Value) //  both are DBNull.Value

            return true;

    if (A == DBNull.Value || B == DBNull.Value) //  only one is BNull.Value

            return false;

    return (A.Equals(B));  // value type standard comparison

}

public DataTable SelectDistinct(DataTable SourceTable, string FieldName)

{

    // Create a Datatable – datatype same as FieldName

    DataTable dt = new DataTable(SourceTable.TableName);

    dt.Columns.Add(FieldName, SourceTable.Columns[FieldName].DataType);

    // Loop each row & compare each value with one another

    // Add it to datatable if the values are mismatch

    object LastValue = null;

    foreach (DataRow dr in SourceTable.Select("", FieldName))

    {

        if (LastValue == null || !(ColumnEqual(LastValue,dr[FieldName])))

        {

            LastValue = dr[FieldName];

           dt.Rows.Add(new object[] { LastValue });

        }

    }

    return dt;

}

#endregion

Example:

Consider the following Dataset dsOrders,

Get distinct Product from this Dataset, 

DataTable distinctDT = SelectDistinct(dsOrders.Tables[0], "Product");

For CashMode,

DataTable distinctDT = SelectDistinct(dsOrders.Tables[0], "CashMode");

Output: