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How to split a file into many files by using groups (LINQ) (C#)

  • Članak
  • 2 min. za čitanje

This example shows one way to merge the contents of two files and then create a set of new files that organize the data in a new way.

To create the data files

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

Example

class SplitWithGroups  
{  
    static void Main()  
    {  
        string[] fileA = System.IO.File.ReadAllLines(@"../../../names1.txt");  
        string[] fileB = System.IO.File.ReadAllLines(@"../../../names2.txt");  
  
        // Concatenate and remove duplicate names based on  
        // default string comparer  
        var mergeQuery = fileA.Union(fileB);  
  
        // Group the names by the first letter in the last name.  
        var groupQuery = from name in mergeQuery  
                         let n = name.Split(',')  
                         group name by n[0][0] into g  
                         orderby g.Key  
                         select g;  
  
        // Create a new file for each group that was created  
        // Note that nested foreach loops are required to access  
        // individual items with each group.  
        foreach (var g in groupQuery)  
        {  
            // Create the new file name.  
            string fileName = @"../../../testFile_" + g.Key + ".txt";  
  
            // Output to display.  
            Console.WriteLine(g.Key);  
  
            // Write file.  
            using (System.IO.StreamWriter sw = new System.IO.StreamWriter(fileName))  
            {  
                foreach (var item in g)  
                {  
                    sw.WriteLine(item);  
                    // Output to console for example purposes.  
                    Console.WriteLine("   {0}", item);  
                }  
            }  
        }  
        // Keep console window open in debug mode.  
        Console.WriteLine("Files have been written. Press any key to exit");  
        Console.ReadKey();  
    }  
}  
/* Output:
    A  
       Aw, Kam Foo  
    B  
       Bankov, Peter  
       Beebe, Ann  
    E  
       El Yassir, Mehdi  
    G  
       Garcia, Hugo  
       Guy, Wey Yuan  
       Garcia, Debra  
       Gilchrist, Beth  
       Giakoumakis, Leo  
    H  
       Holm, Michael  
    L  
       Liu, Jinghao  
    M  
       Myrcha, Jacek  
       McLin, Nkenge  
    N  
       Noriega, Fabricio  
    P  
       Potra, Cristina  
    T  
       Toyoshima, Tim  
 */

The program writes a separate file for each group in the same folder as the data files.

Compiling the Code

Create a C# console application project, with using directives for the System.Linq and System.IO namespaces.

See also