IEnumerable <T> with anonymous methods

I dont know how to get rid of this error ?

Error 1 Using the generic type 'System.Collections.Generic.IEnumerable' requires 1 type arguments C:\Users\huzaifa.gain\documents\visual studio 2010\Projects\VendInvoiceImport\VendInvoiceImport\Program.cs 34 24 VendInvoiceImport

private static IEnumerable<string , string >  DistinctInvoiceNumber(DataTable   VendorInvoiceStagingTable)
       {
           var InvoiceLinecollection = VendorInvoiceStagingTable.AsEnumerable()开发者_高级运维.Select(t => new {  number = t.Field<string>(VendInvoice.Number),LineNumber = t.Field<string>(VendInvoice.LineNumber)}).Distinct();
        return InvoiceLinecollection;
      }

Your Linq query returns an sequence of anonymous type, but methods can't return anonymous types. You have several options:

• return an IEnumerable<Tuple<string, string>>

  private static IEnumerable<Tuple<string, string>>  DistinctInvoiceNumber(DataTable   VendorInvoiceStagingTable)
  {
      var InvoiceLinecollection = VendorInvoiceStagingTable
                                      .AsEnumerable()
                                      .Select(t => Tuple.Create(t.Field<string>(VendInvoice.Number), t.Field<string>(VendInvoice.LineNumber)))
                                       .Distinct();
      return InvoiceLinecollection;
  }
  

• return a IDictionary<string, string> as suggested in another answer (assuming your query doesn't return duplicate keys)

  private static IDictionary<string, string> DistinctInvoiceNumber(DataTable   VendorInvoiceStagingTable)
  {
      var InvoiceLinecollection = VendorInvoiceStagingTable
                                      .AsEnumerable()
                                      .Select(t => Tuple.Create(t.Field<string>(VendInvoice.Number), t.Field<string>(VendInvoice.LineNumber)))
                                      .Distinct()
                                      .ToDictionary(t => t.Item1, t => t.Item2);
      return InvoiceLinecollection;
  }
  

• create a class for this purpose with 2 string properties and return a sequence of that class

  private static IEnumerable<InvoiceLine>  DistinctInvoiceNumber(DataTable   VendorInvoiceStagingTable)
  {
      var InvoiceLinecollection = VendorInvoiceStagingTable
                                      .AsEnumerable()
                                      .Select(t => new InvoiceLine(t.Field<string>(VendInvoice.Number), t.Field<string>(VendInvoice.LineNumber)))
                                      .Distinct();
      return InvoiceLinecollection;
  }
  

Why you do not use Dictionary<string, string> instead?

private static Dictionary<string , string >  DistinctInvoiceNumber(DataTable   VendorInvoiceStagingTable)
       {
           var InvoiceLinecollection = VendorInvoiceStagingTable.AsEnumerable().Select(t => new {  number = t.Field<string>(VendInvoice.Number),LineNumber = 
                 t.Field<string>(VendInvoice.LineNumber)}).ToDictionary();
            return InvoiceLinecollection;
          }