MapReduce

BlogPostCountByAuthorTask

public class BlogPostCountByAuthorTask : MapReduceTask<BlogPost, BlogPostCountByAuthorTask.PostCountResult>
    {
        public class PostCountResult
        {
            public string AuthorName { get; set; }
            public int PostCount { get; set; }
        }

        public BlogPostCountByAuthorTask()
        {
            Map = posts => from post in posts
                           select new 
                           {
                               AuthorName = post.AuthorName, 
                               PostCount = 1 
                           };

           
            Reduce = results => from agg in results
                                group agg by agg.AuthorName into authors
                                select new PostCountResult
                                {
                                    AuthorName = authors.Key,
                                    PostCount = authors.Sum(x => x.PostCount)
                                };
        }
    }

MapReducingTests

namespace MapReducing.Tests
{
    public class MapReducingTests
    {
        private BlogPost[] blogPosts = new[]
        {
            new BlogPost { AuthorName = "jnelson" },
            new BlogPost { AuthorName = "jnelson" },
            new BlogPost { AuthorName = "jnelson" },
            new BlogPost { AuthorName = "jnelson" },
            new BlogPost { AuthorName = "chicks" },
            new BlogPost { AuthorName = "chicks" },
            new BlogPost { AuthorName = "chicks" },
            new BlogPost { AuthorName = "cgossler" },
            new BlogPost { AuthorName = "lharper" },
            new BlogPost { AuthorName = "lharper" }
        };
            
        [Fact]
        public void BlogPostCountByAuthorTask_Returns_Correct_Count()
        {
            var mapReduceTask = new BlogPostCountByAuthorTask();

            var results = mapReduceTask.Execute(blogPosts);
            Console.WriteLine(results.Count());
            Assert.Equal(4, results.Single(result => result.AuthorName == "jnelson").PostCount);
            Assert.Equal(3, results.Single(result => result.AuthorName == "chicks").PostCount);
            Assert.Equal(1, results.Single(result => result.AuthorName == "cgossler").PostCount);
            Assert.Equal(2, results.Single(result => result.AuthorName == "lharper").PostCount);
        }
    }
}