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How to: Combine and Compare String Collections (LINQ)

This example shows how to merge files that contain lines of text and then sort the results. Specifically, it shows how to perform a simple concatenation, a union, and an intersection on the two sets of text lines.

To set up the project and the text files

  1. Copy these names into a text file that is named names1.txt and save it in your solution folder:

    Bankov, Peter
    Holm, Michael
    Garcia, Hugo
    Potra, Cristina
    Noriega, Fabricio
    Aw, Kam Foo
    Beebe, Ann
    Toyoshima, Tim
    Guy, Wey Yuan
    Garcia, Debra
    
  2. Copy these names into a text file that is named names2.txt and save it in your solution folder. Note that the two files have some names in common.

    Liu, Jinghao
    Bankov, Peter
    Holm, Michael
    Garcia, Hugo
    Beebe, Ann
    Gilchrist, Beth
    Myrcha, Jacek
    Giakoumakis, Leo
    McLin, Nkenge
    El Yassir, Mehdi
    


    class MergeStrings
    {
        static void Main(string[] args)
        {
            //Put text files in your solution folder
            string[] fileA = System.IO.File.ReadAllLines(@"../../../names1.txt");
            string[] fileB = System.IO.File.ReadAllLines(@"../../../names2.txt");

            //Simple concatenation and sort. Duplicates are preserved.
            IEnumerable<string> concatQuery =
                fileA.Concat(fileB).OrderBy(s => s);

            // Pass the query variable to another function for execution.
            OutputQueryResults(concatQuery, "Simple concatenate and sort. Duplicates are preserved:");

            // Concatenate and remove duplicate names based on
            // default string comparer.
            IEnumerable<string> uniqueNamesQuery =
                fileA.Union(fileB).OrderBy(s => s);
            OutputQueryResults(uniqueNamesQuery, "Union removes duplicate names:");

            // Find the names that occur in both files (based on
            // default string comparer).
            IEnumerable<string> commonNamesQuery =
                fileA.Intersect(fileB);
            OutputQueryResults(commonNamesQuery, "Merge based on intersect:");

            // Find the matching fields in each list. Merge the two 
            // results by using Concat, and then
            // sort using the default string comparer.
            string nameMatch = "Garcia";

            IEnumerable<String> tempQuery1 =
                from name in fileA
                let n = name.Split(',')
                where n[0] == nameMatch
                select name;

            IEnumerable<string> tempQuery2 =
                from name2 in fileB
                let n2 = name2.Split(',')
                where n2[0] == nameMatch
                select name2;

            IEnumerable<string> nameMatchQuery =
                tempQuery1.Concat(tempQuery2).OrderBy(s => s);
            OutputQueryResults(nameMatchQuery, String.Format("Concat based on partial name match \"{0}\":", nameMatch));

            // Keep the console window open in debug mode.
            Console.WriteLine("Press any key to exit");
            Console.ReadKey();
        }

        static void OutputQueryResults(IEnumerable<string> query, string message)
        {
            Console.WriteLine(System.Environment.NewLine + message);
            foreach (string item in query)
            {
                Console.WriteLine(item);
            }
            Console.WriteLine("{0} total names in list", query.Count());
        }
    }
    /* Output:
        Simple concatenate and sort. Duplicates are preserved:
        Aw, Kam Foo
        Bankov, Peter
        Bankov, Peter
        Beebe, Ann
        Beebe, Ann
        El Yassir, Mehdi
        Garcia, Debra
        Garcia, Hugo
        Garcia, Hugo
        Giakoumakis, Leo
        Gilchrist, Beth
        Guy, Wey Yuan
        Holm, Michael
        Holm, Michael
        Liu, Jinghao
        McLin, Nkenge
        Myrcha, Jacek
        Noriega, Fabricio
        Potra, Cristina
        Toyoshima, Tim
        20 total names in list

        Union removes duplicate names:
        Aw, Kam Foo
        Bankov, Peter
        Beebe, Ann
        El Yassir, Mehdi
        Garcia, Debra
        Garcia, Hugo
        Giakoumakis, Leo
        Gilchrist, Beth
        Guy, Wey Yuan
        Holm, Michael
        Liu, Jinghao
        McLin, Nkenge
        Myrcha, Jacek
        Noriega, Fabricio
        Potra, Cristina
        Toyoshima, Tim
        16 total names in list

        Merge based on intersect:
        Bankov, Peter
        Holm, Michael
        Garcia, Hugo
        Beebe, Ann
        4 total names in list

        Concat based on partial name match "Garcia":
        Garcia, Debra
        Garcia, Hugo
        Garcia, Hugo
        3 total names in list
*/


  • Create a Visual Studio project that targets the .NET Framework version 3.5. By default, the project has a reference to System.Core.dll and a using directive (C#) or Imports statement (Visual Basic) for the System.Linq namespace. In C# projects, add a using directive for the System.IO namespace.

  • Copy this code into your project.

  • Press F5 to compile and run the program.

  • Press any key to exit the console window.

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