C# - Datatable search by LINQ to avoid duplication

To search a DataTable using LINQ and avoid duplication in C#, you can use LINQ queries to filter and select unique rows based on specific criteria. Here's a guide on how to achieve this:

1. Create and Populate a DataTable

First, let's create and populate a DataTable with some sample data.

using System; using System.Data; using System.Linq; public class Program { public static void Main() { // Create a DataTable DataTable table = new DataTable(); table.Columns.Add("Id", typeof(int)); table.Columns.Add("Name", typeof(string)); table.Columns.Add("Category", typeof(string)); // Populate the DataTable with sample data table.Rows.Add(1, "Item A", "Category 1"); table.Rows.Add(2, "Item B", "Category 2"); table.Rows.Add(3, "Item C", "Category 1"); table.Rows.Add(4, "Item A", "Category 1"); // Duplicate in terms of Name and Category table.Rows.Add(5, "Item B", "Category 2"); // Duplicate in terms of Name and Category // Display the data before removing duplicates Console.WriteLine("Original DataTable:"); DisplayDataTable(table); // Remove duplicates using LINQ var distinctTable = GetDistinctRows(table); // Display the data after removing duplicates Console.WriteLine("\nDataTable with duplicates removed:"); DisplayDataTable(distinctTable); } private static DataTable GetDistinctRows(DataTable table) { var distinctRows = table.AsEnumerable() .GroupBy(row => new { Name = row["Name"], Category = row["Category"] }) .Select(g => g.First()) .CopyToDataTable(); return distinctRows; } private static void DisplayDataTable(DataTable table) { foreach (DataRow row in table.Rows) { Console.WriteLine($"{row["Id"],-5} {row["Name"],-10} {row["Category"]}"); } } } 

Explanation

• Create and Populate DataTable: We create a DataTable and add columns and rows with sample data, including duplicates.
• Display the DataTable: A helper method DisplayDataTable prints the contents of the DataTable.
• Remove Duplicates Using LINQ:
  • GroupBy: Groups rows by a composite key created from the columns that define uniqueness (e.g., Name and Category).
  • Select: Selects the first row from each group, effectively removing duplicates.
  • CopyToDataTable: Converts the result back to a DataTable.

Notes

• Ensure Unique Key: Adjust the GroupBy clause to reflect the columns that determine uniqueness in your context.
• Handling Large Data: For very large datasets, consider performance implications and optimize accordingly.

By following this approach, you can effectively search and remove duplicate rows from a DataTable using LINQ in C#.

Examples

1. "C# DataTable search unique rows with LINQ"

   Description: Use LINQ to find unique rows in a DataTable based on a specific column to avoid duplication.

   Code:

   using System; using System.Data; using System.Linq; class Program { static void Main() { DataTable table = new DataTable(); table.Columns.Add("ID", typeof(int)); table.Columns.Add("Name", typeof(string)); table.Rows.Add(1, "Alice"); table.Rows.Add(2, "Bob"); table.Rows.Add(1, "Alice"); // Duplicate var distinctRows = table.AsEnumerable() .GroupBy(row => row.Field<int>("ID")) .Select(group => group.First()); foreach (var row in distinctRows) { Console.WriteLine($"{row["ID"]}, {row["Name"]}"); } } } 

2. "C# DataTable filter distinct rows using LINQ"

   Description: Filter distinct rows from a DataTable using LINQ based on multiple columns.

   Code:

   using System; using System.Data; using System.Linq; class Program { static void Main() { DataTable table = new DataTable(); table.Columns.Add("ID", typeof(int)); table.Columns.Add("Name", typeof(string)); table.Columns.Add("Age", typeof(int)); table.Rows.Add(1, "Alice", 30); table.Rows.Add(2, "Bob", 25); table.Rows.Add(1, "Alice", 30); // Duplicate var distinctRows = table.AsEnumerable() .GroupBy(row => new { ID = row.Field<int>("ID"), Name = row.Field<string>("Name") }) .Select(group => group.First()); foreach (var row in distinctRows) { Console.WriteLine($"{row["ID"]}, {row["Name"]}, {row["Age"]}"); } } } 

3. "C# DataTable find unique values in column with LINQ"

   Description: Find unique values in a specific column of a DataTable using LINQ.

   Code:

   using System; using System.Data; using System.Linq; class Program { static void Main() { DataTable table = new DataTable(); table.Columns.Add("Name", typeof(string)); table.Rows.Add("Alice"); table.Rows.Add("Bob"); table.Rows.Add("Alice"); // Duplicate var uniqueNames = table.AsEnumerable() .Select(row => row.Field<string>("Name")) .Distinct(); foreach (var name in uniqueNames) { Console.WriteLine(name); } } } 

4. "C# DataTable select distinct rows with LINQ"

   Description: Select distinct rows from a DataTable using LINQ, avoiding duplication based on multiple columns.

   Code:

   using System; using System.Data; using System.Linq; class Program { static void Main() { DataTable table = new DataTable(); table.Columns.Add("ID", typeof(int)); table.Columns.Add("Name", typeof(string)); table.Rows.Add(1, "Alice"); table.Rows.Add(2, "Bob"); table.Rows.Add(1, "Alice"); // Duplicate var distinctRows = table.AsEnumerable() .Distinct(DataRowComparer.Default); foreach (var row in distinctRows) { Console.WriteLine($"{row["ID"]}, {row["Name"]}"); } } } 

5. "C# DataTable search for unique rows by multiple columns with LINQ"

   Description: Search for unique rows based on multiple columns in a DataTable using LINQ.

   Code:

   using System; using System.Data; using System.Linq; class Program { static void Main() { DataTable table = new DataTable(); table.Columns.Add("ID", typeof(int)); table.Columns.Add("Name", typeof(string)); table.Columns.Add("City", typeof(string)); table.Rows.Add(1, "Alice", "New York"); table.Rows.Add(2, "Bob", "Chicago"); table.Rows.Add(1, "Alice", "New York"); // Duplicate var uniqueRows = table.AsEnumerable() .GroupBy(row => new { ID = row.Field<int>("ID"), Name = row.Field<string>("Name") }) .Select(group => group.First()); foreach (var row in uniqueRows) { Console.WriteLine($"{row["ID"]}, {row["Name"]}, {row["City"]}"); } } } 

6. "C# DataTable remove duplicates by column with LINQ"

   Description: Remove duplicate rows from a DataTable based on a specific column using LINQ.

   Code:

   using System; using System.Data; using System.Linq; class Program { static void Main() { DataTable table = new DataTable(); table.Columns.Add("Name", typeof(string)); table.Columns.Add("Age", typeof(int)); table.Rows.Add("Alice", 30); table.Rows.Add("Bob", 25); table.Rows.Add("Alice", 30); // Duplicate var distinctRows = table.AsEnumerable() .GroupBy(row => row.Field<string>("Name")) .Select(group => group.First()); foreach (var row in distinctRows) { Console.WriteLine($"{row["Name"]}, {row["Age"]}"); } } } 

7. "C# DataTable unique rows by combination of columns with LINQ"

   Description: Get unique rows from a DataTable based on a combination of columns using LINQ.

   Code:

   using System; using System.Data; using System.Linq; class Program { static void Main() { DataTable table = new DataTable(); table.Columns.Add("ID", typeof(int)); table.Columns.Add("Name", typeof(string)); table.Columns.Add("Age", typeof(int)); table.Rows.Add(1, "Alice", 30); table.Rows.Add(2, "Bob", 25); table.Rows.Add(1, "Alice", 30); // Duplicate var uniqueRows = table.AsEnumerable() .GroupBy(row => new { ID = row.Field<int>("ID"), Name = row.Field<string>("Name"), Age = row.Field<int>("Age") }) .Select(group => group.First()); foreach (var row in uniqueRows) { Console.WriteLine($"{row["ID"]}, {row["Name"]}, {row["Age"]}"); } } } 

8. "C# DataTable avoid duplicates using LINQ with complex conditions"

   Description: Avoid duplicate rows in a DataTable using LINQ with complex conditions.

   Code:

   using System; using System.Data; using System.Linq; class Program { static void Main() { DataTable table = new DataTable(); table.Columns.Add("ID", typeof(int)); table.Columns.Add("Name", typeof(string)); table.Columns.Add("Age", typeof(int)); table.Rows.Add(1, "Alice", 30); table.Rows.Add(2, "Bob", 25); table.Rows.Add(1, "Alice", 30); // Duplicate table.Rows.Add(1, "Alice", 35); // Different age var distinctRows = table.AsEnumerable() .GroupBy(row => new { ID = row.Field<int>("ID"), Name = row.Field<string>("Name") }) .Select(group => group.OrderByDescending(r => r.Field<int>("Age")).First()); foreach (var row in distinctRows) { Console.WriteLine($"{row["ID"]}, {row["Name"]}, {row["Age"]}"); } } } 

9. "C# DataTable LINQ to find rows with unique combination of columns"

   Description: Use LINQ to find rows with a unique combination of specified columns in a DataTable.

   Code:

   using System; using System.Data; using System.Linq; class Program { static void Main() { DataTable table = new DataTable(); table.Columns.Add("ID", typeof(int)); table.Columns.Add("Name", typeof(string)); table.Columns.Add("City", typeof(string)); table.Rows.Add(1, "Alice", "New York"); table.Rows.Add(2, "Bob", "Chicago"); table.Rows.Add(1, "Alice", "Chicago"); // Different city, same ID var uniqueRows = table.AsEnumerable() .GroupBy(row => new { ID = row.Field<int>("ID"), City = row.Field<string>("City") }) .Select(group => group.First()); foreach (var row in uniqueRows) { Console.WriteLine($"{row["ID"]}, {row["Name"]}, {row["City"]}"); } } } 

10. "C# DataTable remove duplicates based on multiple columns with LINQ"

    Description: Remove duplicate rows from a DataTable based on multiple columns using LINQ.

    Code:

    using System; using System.Data; using System.Linq; class Program { static void Main() { DataTable table = new DataTable(); table.Columns.Add("ID", typeof(int)); table.Columns.Add("Name", typeof(string)); table.Columns.Add("City", typeof(string)); table.Rows.Add(1, "Alice", "New York"); table.Rows.Add(2, "Bob", "Chicago"); table.Rows.Add(1, "Alice", "New York"); // Duplicate var distinctRows = table.AsEnumerable() .GroupBy(row => new { ID = row.Field<int>("ID"), Name = row.Field<string>("Name"), City = row.Field<string>("City") }) .Select(group => group.First()); foreach (var row in distinctRows) { Console.WriteLine($"{row["ID"]}, {row["Name"]}, {row["City"]}"); } } } 

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