CSharp - Except for DataTable

Introduction

The Except operator produces a sequence of DataRow objects that are in the first sequence of DataRow objects that do not exist in the second sequence.

Prototypes

public static IEnumerable<T> Except<T> (
  this IEnumerable<T> first,
  IEnumerable<T> second,
  IEqualityComparer<T> comparer);

In this example, we call the Except operator twice.

The first time, we pass the System.Data.DataRowComparer.Default comparer object.

The second time we call the Except operator, we will not pass the comparer object.

We create two DataTable objects that are populated from the Student arrays.

We create sequences from each DataTable object by calling the AsEnumerable method.

Then call the Except operator on the two sequences and display the results of each.

Demo

using System;
using System.Linq;
using System.Collections;
using System.Collections.Generic;
using System.Data;

class Program//from  ww w  . j a va 2 s  . c o m
{
    static void Main(string[] args)
    {
        Student[] students = {
          new Student { Id = 1, Name = "Joe Ruby" },
          new Student { Id = 7, Name = "Apache Python" },
          new Student { Id = 13, Name = "Scala Sinclair" },
          new Student { Id = 72, Name = "Django SQL" }
        };

                Student[] students2 = {
          new Student { Id = 5, Name = "Abe Html" },
          new Student { Id = 7, Name = "Apache Python" },
          new Student { Id = 29, Name = "Future Man" },
          new Student { Id = 72, Name = "Django SQL" }
        };

        DataTable dt1 = GetDataTable(students);
        IEnumerable<DataRow> seq1 = dt1.AsEnumerable();
        DataTable dt2 = GetDataTable(students2);
        IEnumerable<DataRow> seq2 = dt2.AsEnumerable();

        IEnumerable<DataRow> except =
          seq1.Except(seq2, System.Data.DataRowComparer.Default);

        Console.WriteLine("{0}Results of Except() with comparer{0}",
          System.Environment.NewLine);

        OutputDataTableHeader(dt1, 15);

        foreach (DataRow dataRow in except)
        {
            Console.WriteLine("{0,-15}{1,-15}",
              dataRow.Field<int>(0),
              dataRow.Field<string>(1));
        }

        except = seq1.Except(seq2);

        Console.WriteLine("{0}Results of Except() without comparer{0}",
          System.Environment.NewLine);

        OutputDataTableHeader(dt1, 15);

        foreach (DataRow dataRow in except)
        {
            Console.WriteLine("{0,-15}{1,-15}",
              dataRow.Field<int>(0),
              dataRow.Field<string>(1));
        }
    }
    static void OutputDataTableHeader(DataTable dt, int columnWidth)
    {
        string format = string.Format("{0}0,-{1}{2}", "{", columnWidth, "}");

        //  Display the column headings.
        foreach (DataColumn column in dt.Columns)
        {
            Console.Write(format, column.ColumnName);
        }
        Console.WriteLine();
        foreach (DataColumn column in dt.Columns)
        {
            for (int i = 0; i < columnWidth; i++)
            {
                Console.Write("=");
            }
        }
        Console.WriteLine();
    }
    static DataTable GetDataTable(Student[] students)
    {
        DataTable table = new DataTable();

        table.Columns.Add("Id", typeof(Int32));
        table.Columns.Add("Name", typeof(string));

        foreach (Student student in students)
        {
            table.Rows.Add(student.Id, student.Name);
        }

        return (table);
    }
}

class Student
{
    public int Id;
    public string Name;
}

Result