Gapotchenko.FX.Linq

Gapotchenko.FX.Linq

The module provides primitives for functional processing of data sequences.

Memoize

Memoization is a pillar of functional data processing. You already met it quite often albeit in somewhat masked forms.

Gapotchenko.FX.Linq module provides the Memoize() extension method for IEnumerable<T> types. You can use it like this:

using Gapotchenko.FX.Linq;

var files = Directory.EnumerateFiles(".", "*.txt").Select(Path.GetFileName).Memoize();

Console.WriteLine("A text file with an upper case letter is present: {0}", files.Any(x => x.Any(char.IsUpper)));
Console.WriteLine("A text file with a name longer than 12 letters is present: {0}", files.Any(x => x.Length > 12));

Memoize() caches the already retrieved elements of a sequence, and does it lazily.

.NET developers often use ToList() and ToArray() methods for the very same purpose. But those methods are eager, as they retrieve all elements of a sequence in one shot. This often leads to suboptimal performance of an otherwise sound functional algorithm.

Memoize() solves that. This is the method you are going to use the most for LINQ caching.

ScalarOrDefault

The second most popular primitive provided by Gapotchenko.FX.Linq module is ScalarOrDefault() method. It is similar to SingleOrDefault() from conventional .NET but with one big difference: it does not throw an exception when sequence contains multiple elements.

SingleOrDefault() Semantics

using System.Linq;

new string[0].SingleOrDefault(); // returns null
new[] { "A" }.SingleOrDefault(); // returns "A"
new[] { "A", "B" }.SingleOrDefault(); // throws an exception 😞

ScalarOrDefault() Semantics

using Gapotchenko.FX.Linq;

new string[0].ScalarOrDefault(); // returns null
new[] { "A" }.ScalarOrDefault(); // returns "A"
new[] { "A", "B" }.ScalarOrDefault(); // returns null 👍

In practice, ScalarOrDefault() semantics is a big win as it allows to safely determine whether a given query converges to a scalar result.

DistinctBy

Returns distinct elements from a sequence by using the default equality comparer on the keys extracted by a specified selector function.

The method is similar to Distinct() method provided by the stock System.Linq namespace, but allows to specify a selector function in order to differentiate the elements by a specific criteria.

Let's take a look at example:

using Gapotchenko.FX.Linq;

var source = new[]
{
    new { FirstName = "Alex", LastName = "Cooper" },
    new { FirstName = "John", LastName = "Walker" },
    new { FirstName = "Alex", LastName = "The Great" },
    new { FirstName = "Jeremy", LastName = "Doer" }
};

var query = source.DistinctBy(x => x.FirstName);

foreach (var i in query)
    Console.WriteLine(i);

The code produces the following output:

{ FirstName = Alex, LastName = Cooper }
{ FirstName = John, LastName = Walker }
{ FirstName = Jeremy, LastName = Doer }

MinBy/MaxBy

Returns a minimum/maximum value in a sequence according to a specified key selector function.

Let's take a look at example:

using Gapotchenko.FX.Linq;

var source = new[]
{
    new { FirstName = "Alex", LastName = "Cooper", Age = 45 },
    new { FirstName = "John", LastName = "Walker", Age = 17 },
    new { FirstName = "Alex", LastName = "The Great", Age = 1500 },
    new { FirstName = "Jeremy", LastName = "Doer", Age = 29 }
};

Console.WriteLine("The oldest person: {0}", source.MaxBy(x => x.Age));
Console.WriteLine("The youngest person: {0}", source.MinBy(x => x.Age));

The code produces the following output:

The oldest person: { FirstName = Alex, LastName = The Great, Age = 1500 }
The youngest person: { FirstName = John, LastName = Walker, Age = 17 }

MinOrDefault/MaxOrDefault

These methods augment the semantics of conventional Min and Max methods, allowing to return the default value when the input sequence is empty. Conventional Min and Max methods just throw an exception in that case.

Usage

Gapotchenko.FX.Linq module is available as a NuGet package:

PM> Install-Package Gapotchenko.FX.Linq

Other Modules

Let's continue with a look at some other modules provided by Gapotchenko.FX:

• Gapotchenko.FX
• Gapotchenko.FX.AppModel.Information
• Gapotchenko.FX.Collections
• Gapotchenko.FX.Console
• Gapotchenko.FX.Diagnostics
• Gapotchenko.FX.IO
• ➴ Gapotchenko.FX.Linq
• Gapotchenko.FX.Math
• Gapotchenko.FX.Memory
• Gapotchenko.FX.Text
• Gapotchenko.FX.Threading

Or look at the full list of modules.