Find the count of a weekday between two dates without iterating/looping

Single line in Linq

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This gets you the number of weekdays, i.e., Monday to Friday between given two dates.
[VB]

Dim dt1 As New Date(2011, 1, 1)
Dim dt2 As New Date(2011, 1, 15)
Dim days As Integer = (From d As Date In _
  (Enumerable.Range(0, 1 + dt2.Subtract(dt1).Days).Select(Function(offset) dt1.AddDays(offset)).ToArray()) _
  Where d.DayOfWeek >= DayOfWeek.Monday And d.DayOfWeek <= DayOfWeek.Friday Select 1).Sum

[C#]

DateTime dt1 = new DateTime(2011, 1, 1);
DateTime dt2 = new DateTime(2011, 1, 15);
int days = (from d in (Enumerable.Range(0, 1 + dt2.Subtract(dt1).Days).Select(offset => dt1.AddDays(offset)).ToArray())where d.DayOfWeek >= DayOfWeek.Monday & d.DayOfWeek <= DayOfWeek.Friday1).Sum;

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You can easily modify it to get the count of a particular day as,
[VB]

Dim dt1 As New Date(2011, 1, 1)
Dim dt2 As New Date(2011, 1, 15)
Dim days As Integer = (From d As Date In _
  (Enumerable.Range(0, 1 + dt2.Subtract(dt1).Days).Select(Function(offset) dt1.AddDays(offset)).ToArray()) _
  Where d.DayOfWeek = DayOfWeek.Monday Select 1).Sum

[C#]

DateTime dt1 = new DateTime(2011, 1, 1);
DateTime dt2 = new DateTime(2011, 1, 15);
int days = (from d in (Enumerable.Range(0, 1 + dt2.Subtract(dt1).Days).Select(offset => dt1.AddDays(offset)).ToArray())where d.DayOfWeek == DayOfWeek.Monday).Sum;

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See here, Enumerable.Range gets you the array of dates between given dates. You can apply your conditions and get different results using Linq on it.