How to: Select distinct values from Dataset

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