CSharp - Parallel LINQ AsUnordered

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Introduction

AsUnordered operator undoes the effect of applying the AsOrdered operator.

This can be useful in multipart queries where you need ordering in only one part.

Prototypes 

public static ParallelQuery<T AsUnordered<T>(
          this ParallelQuery<T> source
)

The following code demonstrates the use of the AsUnordered operator in a two-stage PLINQ query.

Demo

using System;
using System.Linq;
using System.Collections;
using System.Collections.Generic;

class Program/*from  w  w w.ja  v  a 2s  .  co m*/
{
    static void Main(string[] args)
    {
              string[] codeNames = {"Python", "Java", "Javascript", "Bash", "C++", "Oracle"};
        
        IEnumerable<string> results = codeNames
            .AsParallel()
            .AsOrdered()
            .Where(p => p.Contains('o'))
            .Take(5)
            .AsUnordered()
            .Where(p => p.Contains('e'))
            .Select(p => p);
        
        foreach (string president in results) {
            Console.WriteLine("Match: {0}", president);
        }
    }
}

In this code we first find all the codeNames' names that contain the letter o preserving the order of the results using the AsOrdered operator.

We call AsUnordered to avoid PLINQ incurring the overhead of sorting the results.