How to sort or filter text data by any word or field (LINQ) (C#)

The following example shows how to sort lines of structured text, such as comma-separated values, by any field in the line. The field may be dynamically specified at run time. Assume that the fields in scores.csv represent a student's ID number, followed by a series of four test scores.

To create a file that contains data

1. Copy the scores.csv data from the topic How to join content from dissimilar files (LINQ) (C#) and save it to your solution folder.

Example

public class SortLines  
{  
    static void Main()  
    {  
        // Create an IEnumerable data source  
        string[] scores = System.IO.File.ReadAllLines(@"../../../scores.csv");  
  
        // Change this to any value from 0 to 4.  
        int sortField = 1;  
  
        Console.WriteLine("Sorted highest to lowest by field [{0}]:", sortField);  
  
        // Demonstrates how to return query from a method.  
        // The query is executed here.  
        foreach (string str in RunQuery(scores, sortField))  
        {  
            Console.WriteLine(str);  
        }  
    }  
  
    // Returns the query variable, not query results!  
    static IEnumerable<string> RunQuery(IEnumerable<string> source, int num)  
    {  
        // Split the string and sort on field[num]  
        var scoreQuery = from line in source  
                         let fields = line.Split(',')  
                         orderby fields[num] descending  
                         select line;  
  
        return scoreQuery;  
    }  
}  
/* Output (if sortField == 1):  
   Sorted highest to lowest by field [1]:  
    116, 99, 86, 90, 94  
    120, 99, 82, 81, 79  
    111, 97, 92, 81, 60  
    114, 97, 89, 85, 82  
    121, 96, 85, 91, 60  
    122, 94, 92, 91, 91  
    117, 93, 92, 80, 87  
    118, 92, 90, 83, 78  
    113, 88, 94, 65, 91  
    112, 75, 84, 91, 39  
    119, 68, 79, 88, 92  
    115, 35, 72, 91, 70  
 */  

This example also demonstrates how to return a query variable from a method.

Compiling the Code

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