LINQ - group/sum multiple columns

Question

Data is a local CSV file that is loaded into an ado.net dataset via OleDB. The table has 40+ columns consisting of invoice details. Each row is a separate line item within an invoice, which can consist of 1 to n rows.

The query is used to group the invoice details into a single row per invoice, totaling the invoice amount and balance due.

The following works, what I'm trying to determine: Is it possible to do this in a single query?

    //group the invoices by invoicenumber and sum the total
//Zoho has a separate record (row) for each item in the invoice
//first select the columns we need into an anon array   
var invoiceSum =
    DSZoho.Tables["Invoices"].AsEnumerable()
    .Select (x => 
        new {  
            InvNumber = x["invoice number"],
            InvTotal = x["item price"],
            Contact = x["customer name"],
            InvDate = x["invoice date"],
            DueDate = x["due date"],
            Balance = x["balance"],
            } );
    //then group and sum
    var invoiceTotals =
        invoiceSum
        .GroupBy (s => new {s.InvNumber, s.Contact, s.InvDate, s.DueDate} )
        .Select (g => 
            new {
                InvNumber = g.Key.InvNumber,
                InvDate = g.Key.InvDate,
                DueDate = g.Key.DueDate,
                Contact = g.Key.Contact,
                InvTotal = g.Sum (x => Math.Round(Convert.ToDecimal(x.InvTotal), 2)),
                Balance = g.Sum (x => Math.Round(Convert.ToDecimal(x.Balance), 2)),
                } );

You can place GroupBy right after first Select, without introducing invoiceTotals variable — Uriil, Feb 22 '14 at 14:15
possible duplicate of [Group By Multiple Columns](http://stackoverflow.com/questions/847066/group-by-multiple-columns) — psubsee2003, Apr 03 '15 at 08:49

score 63 · Accepted Answer · answered Feb 22 '14 at 14:38

You are, in fact, only doing one query when you use the results of invoiceTotals. In the code you are showing you are even not doing a query on the database.

Google "linq deferred execution", it's nifty ;-)

But as Uriil says, you can just combine the statements into one linq query:

var invoiceSum =
DSZoho.Tables["Invoices"].AsEnumerable()
.Select (x => 
    new {  
        InvNumber = x["invoice number"],
        InvTotal = x["item price"],
        Contact = x["customer name"],
        InvDate = x["invoice date"],
        DueDate = x["due date"],
        Balance = x["balance"],
        }
 )
 .GroupBy (s => new {s.InvNumber, s.Contact, s.InvDate, s.DueDate} )
 .Select (g => 
        new {
            InvNumber = g.Key.InvNumber,
            InvDate = g.Key.InvDate,
            DueDate = g.Key.DueDate,
            Contact = g.Key.Contact,
            InvTotal = g.Sum (x => Math.Round(Convert.ToDecimal(x.InvTotal), 2)),
            Balance = g.Sum (x => Math.Round(Convert.ToDecimal(x.Balance), 2)),
            } 
 );

Ah- thanks for the help. 'linq deferred execution' Had not heard the term before either. I appreciate the input and help. — topry, Feb 22 '14 at 14:42

LINQ - group/sum multiple columns

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