.NET Fiddle

CSharp · Console

/Program.cs

using System;
using ChoETL;
using System.Collections.Generic;
using System.Linq;
using System.Text;

public class Program
{
	public static void Main()
	{
		string csv1 = @"col1, col2, col3
val1, val2, val3
val11, val21, val31";
		
		string csv2 = @"col1, col3
val4, val5
val41, val51";
		
		string csv3 = @"col1, col4
val6, val7
val61, val71";
		
		ChoCSVRecordConfiguration config = null;
		List<object> items = new List<object>();
		using (var r1 = ChoCSVReader.LoadText(csv1).WithFirstLineHeader())
		{
			using (var r2 = ChoCSVReader.LoadText(csv2).WithFirstLineHeader())
			{
				using (var r3 = ChoCSVReader.LoadText(csv3).WithFirstLineHeader())
				{
					items.Add(r1.First());
					items.Add(r2.First());
					items.Add(r3.First());
				}
			}
		}

		StringBuilder csv = new StringBuilder();
		using (var w = new ChoCSVWriter(csv)
			   .WithFirstLineHeader()
			   .WithMaxScanRows(5)
			   .ThrowAndStopOnMissingField(false)
			  )
		{
			w.Write(items);

			//Capture configuration for later use to merge CSV files
			config = w.Configuration;
		}

		using (var r1 = ChoCSVReader.LoadText(csv1).WithFirstLineHeader())
		{
			using (var r2 = ChoCSVReader.LoadText(csv2).WithFirstLineHeader())
			{
				using (var r3 = ChoCSVReader.LoadText(csv3).WithFirstLineHeader())
				{
					//use the captured configuration object for merging CSV file
					using (var w = new ChoCSVWriter(Console.Out, config)
						   .WithFirstLineHeader()
						  )
					{
						w.Write(Enumerable.Concat(r1, r2).Concat(r3));
					}
				}
			}
		}
		
	}
}