Add project files.

Books.ConsoleApp.sln

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+
+Microsoft Visual Studio Solution File, Format Version 12.00
+# Visual Studio Version 16
+VisualStudioVersion = 16.0.29509.3
+MinimumVisualStudioVersion = 10.0.40219.1
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Books.ConsoleApp", "Books.ConsoleApp\Books.ConsoleApp.csproj", "{A09D7905-08C5-41F3-ADE6-2037471A2403}"
+EndProject
+Global
+	GlobalSection(SolutionConfigurationPlatforms) = preSolution
+		Debug|Any CPU = Debug|Any CPU
+		Release|Any CPU = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(ProjectConfigurationPlatforms) = postSolution
+		{A09D7905-08C5-41F3-ADE6-2037471A2403}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{A09D7905-08C5-41F3-ADE6-2037471A2403}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{A09D7905-08C5-41F3-ADE6-2037471A2403}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{A09D7905-08C5-41F3-ADE6-2037471A2403}.Release|Any CPU.Build.0 = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(SolutionProperties) = preSolution
+		HideSolutionNode = FALSE
+	EndGlobalSection
+	GlobalSection(ExtensibilityGlobals) = postSolution
+		SolutionGuid = {6F1B272A-118E-4F00-8E83-C7C02A973BD2}
+	EndGlobalSection
+EndGlobal

Books.ConsoleApp/Books.ConsoleApp.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>netcoreapp3.0</TargetFramework>
+  </PropertyGroup>
+
+</Project>

Books.ConsoleApp/Program.cs

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+using System;
+using System.Collections.Generic;
+using System.Globalization;
+
+namespace Books.ConsoleApp
+{
+    class Program
+    {
+        List<BooksByAuthor> BooksByAuthorCatalogue = null;
+        static void Main(string[] args)
+        {
+            Book[] books = BookSource.Read();
+            BooksByAuthorCatalogue = new List<BooksByAuthor>();
+
+            for (int i = 0; i < books.Length; i++)
+            {
+                var book = books[i];
+                if (AuthorIsAlreadyCataloged(book.author))
+                {
+                    // there are some(1 or more) books by this author already found and catalogued
+                    var authorCatalogueIndex = LocateAuthorAlreadyCataloged(book.author);
+
+                    var existingBooks = BooksByAuthorCatalogue[authorCatalogIndex].Books;
+                    existingBooks.Add(book);
+                }
+                else
+                {
+                    CatalogueNewAuthor(book);
+                }
+
+            }
+
+        }
+
+        private static bool AuthorIsAlreadyCataloged(string author)
+        {
+            var authorAlreadyCatalogued = false;
+
+            // we'll iterate over the catalogue to find the author - if athors's already been cataloged
+            for (int j = 0; j < BooksByAuthorCatalogue.Count; j++)
+            {
+                var entry = BooksByAuthorCatalogue[j];
+                if (entry.author == author)
+                {
+                    authorAlreadyCatalogued = true;
+                    break;
+                }
+            }
+
+            return authorAlreadyCatalogued;
+
+        }
+
+        private static int LocateAuthorAlreadyCataloged(string author)
+        {
+            var authorCatalogIndex = 0;
+            
+            // We'll iterate over the cataloge to find the author's index
+            for (int j = 0; j < BooksByAuthorCatalogue.Count; j++)
+            {
+                var entry = BooksByAuthorCatalogue[j];
+                if (entry.Author == author)
+                {
+                    authorCatalogIndex = j;
+                    break;
+                }
+            }
+
+        }
+
+        private static void CatalogueNewAuthor(Book b)
+        {
+            // there are NONE books by this author already found and cataloged
+
+            var newBookList = new List<Book> {b};
+            var authorAndBooks = new BooksByAuthor(b.Author, newBookList);
+
+            BooksByAuthorCatalogue.Add(authorAndBooks);
+        }
+
+        private static void OutputBooksByAuthor()
+        {
+            for (int i = 0; i < BooksByAuthorCatalogue.Count; i++)
+            {
+                BooksByAuthor ba = BooksByAuthorCatalogue[i];
+                Console.Write("Author: {0, -28} Books: ", ba.Author);
+                for (int j = 0; j < ba.Books.Count; j++)
+                {
+                    Console.Write(ba.Books[j].title + ", ");
+                }
+                Console.Write(Environment.NewLine);
+            }
+        }
+
+    }
+
+    public class BooksByAuthor
+    {
+        public readonly string Author;
+        public readonly List<Book> Books;
+
+        public BooksByAuthor(string author, List<Book> books)
+        {
+            Author = author;
+            Books = books;
+        }
+    }
+
+}

Books.ConsoleApp/SearchByAuthor.cs

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+using System;
+using System.Collections.Generic;
+using System.Data.SqlTypes;
+using System.Linq;
+using System.Text;
+
+namespace Books.ConsoleApp
+{
+    public static  class SearchByAuthor
+    {
+        public static IEnumerable<string> MatchBy(
+            IEnumerable<Book> books, string searchCriteria)
+        {
+            return books
+                .ExtractAuthors()
+                .ListAuthorsMatching(searchCriteria);
+        }
+
+        public static IEnumerable<string> SuggestAuthors(
+            IEnumerable<Book> books, int suggestionLength = 5)
+        {
+            return books
+                .ExtractAuthors()
+                .RandomizeOrder()
+                .Take(suggestionLength);
+        }
+
+        public static IEnumerable<Book> ListBooks(IEnumerable<Book> books, string author)
+        {
+            return books
+                .CatalogueByAuthor()
+                .BooksBy(author);
+        }
+
+        public static AuthorCatalogue CatalogueByAuthor(this IEnumerable<Book> books)
+        {
+            return books
+                    .ToLookup(b => b.author)
+                // Mark Twain : {The Adventures of Huckleberry Finn},
+                // Shakespeare: {Othello, Hamlet, ...}
+                // ...
+                ;
+        }
+
+
+        public static IEnumerable<Book> BooksBy(this AuthorCatalogue catalogue, string author)
+        {
+            return catalogue.Contains(author)
+                ? catalogue[author]
+                : Enumerable.Empty<Book>();
+        }
+
+        public static IEnumerable<string> ExtractAuthors(this IEnumerable<Book> books)
+        {
+            return books.Select(b =>
+            {
+                //do stuff here
+                return b.author;
+
+            }).Distinct();
+        }
+
+        public static IEnumerable<string> ListAuthorsMatching(
+            this IEnumerable<string> authors, string searchCriteria)
+        {
+            var partOfNameLower = searchCriteria.ToLower();
+            return authors.Where(a => a.ToLower().Contains(partOfNameLower));
+        }
+
+        private static IOrderedEnumerable<string> RandomizeOrder(this IEnumerable<string> authors)
+        {
+            return authors.OrderBy(_ => Guid.NewGuid());
+        }
+
+    }
+
+    public class AuthorCatalogue
+    {
+    }
+
+    public class Book
+    {
+
+    }
+}