When you start playing with LINQ queries over sequences of elements (e.g. getting min / max value for enumerable source) sooner or later you will come across this one -- the InvalidOperationException (“Sequence contains no elements”).
The problem occurs as by default queries like IEnumerable<T>.Min(…) and IEnumerable<T>.Max(…) do not play nicely if you try to execute them on an empty sequence and just throw the exception described above. Unfortunately these methods do not have a corresponding counterpart like Single(…) / SingleOrDefault(…) that is smart enough to query the sequence if it is not empty or alternatively use the default value without raising an exception.
Basically you got two options now:
- Either perform the check on the enumerable sequence every time you are querying it
- OR integrate the logic in an extension method.
The second approach is much preferable so let’s add the missing link below:
namespace ExtensionMethods
{
using System;
using System.Collections.Generic;
using System.Linq;
public static class IEnumerableExtensions
{
/// <summary>
/// Invokes a transform function on each element of a sequence and returns the minimum Double value
/// if the sequence is not empty; otherwise returns the specified default value.
/// </summary>
/// <typeparam name="TSource">The type of the elements of source.</typeparam>
/// <param name="source">A sequence of values to determine the minimum value of.</param>
/// <param name="selector">A transform function to apply to each element.</param>
/// <param name="defaultValue">The default value.</param>
/// <returns>The minimum value in the sequence or default value if sequence is empty.</returns>
public static double MinOrDefault<TSource>(this IEnumerable<TSource> source, Func<TSource, double> selector, double defaultValue)
{
if (source.Any<TSource>())
return source.Min<TSource>(selector);
return defaultValue;
}
/// <summary>
/// Invokes a transform function on each element of a sequence and returns the maximum Double value
/// if the sequence is not empty; otherwise returns the specified default value.
/// </summary>
/// <typeparam name="TSource">The type of the elements of source.</typeparam>
/// <param name="source">A sequence of values to determine the maximum value of.</param>
/// <param name="selector">A transform function to apply to each element.</param>
/// <param name="defaultValue">The default value.</param>
/// <returns>The maximum value in the sequence or default value if sequence is empty.</returns>
public static double MaxOrDefault<TSource>(this IEnumerable<TSource> source, Func<TSource, double> selector, double defaultValue)
{
if (source.Any<TSource>())
return source.Max<TSource>(selector);
return defaultValue;
}
}
}
Now you only need to add the using ExtensionMethods; directive in your project and you are all set:
Hope this helps.