Determine if Any or All Elements in a Sequence Satisfy a Condition

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Determine if Any or All Elements in a Sequence Satisfy a Condition

The All operator returns true if all elements in a sequence satisfy a condition.

The Any operator returns true if any element in a sequence satisfies a condition.

Example

The following example returns a sequence of customers that have at least one order. The Where/where clause evaluates to true if the given Customer has any Order.

var OrdersQuery =
    from cust in db.Customers
    where cust.Orders.Any()
    select cust;

Dim OrdersQuery = _
    From cust In db.Customers _
    Where cust.Orders.Any() _
    Select cust

The following Visual Basic code determines the list of customers who have not placed orders, and ensures that for every customer in that list, a contact name is provided.

This language is not supported or no code example is available.

Public Sub ContactsAvailable()
    Dim db As New Northwnd("c:\northwnd.mdf")
    Dim result = _
        (From cust In db.Customers _
        Where Not cust.Orders.Any() _
        Select cust).All(AddressOf ContactAvailable)

    If result Then
        Console.WriteLine _
    ("All of the customers who have made no orders have a contact name")
    Else
        Console.WriteLine _
    ("Some customers who have made no orders have no contact name")
    End If
End Sub

Function ContactAvailable(ByVal contact As Object) As Boolean
    Dim cust As Customer = CType(contact, Customer)
    Return (cust.ContactTitle Is Nothing OrElse _
        cust.ContactTitle.Trim().Length = 0)
End Function

The following C# example returns a sequence of customers whose orders have a ShipCity beginning with "C". Also included in the return are customers who have no orders. (By design, the All(Of TSource) operator returns true for an empty sequence.) Customers with no orders are eliminated in the console output by using the Count operator.

var custEmpQuery =
    from cust in db.Customers
    where cust.Orders.All(o => o.ShipCity.StartsWith("C"))
    orderby cust.CustomerID
    select cust;

foreach (Customer custObj in custEmpQuery)
{
    if (custObj.Orders.Count > 0)
        Console.WriteLine("CustomerID: {0}", custObj.CustomerID);
    foreach (Order ordObj in custObj.Orders)
    {
        Console.WriteLine("\t OrderID: {0}; ShipCity: {1}",
            ordObj.OrderID, ordObj.ShipCity);
    }
}

This language is not supported or no code example is available.