How to write only selected class fields into CSV with CsvHelper?

I recently needed to achieve a similar result by determining what fields to include at runtime. This was my approach:

1. Create a mapping file to map which fields I need at runtime by passing in an enum into the class constructor

   public sealed class MyClassMap : CsvClassMap<MyClass>
   {
       public MyClassMap(ClassType type)
       {
           switch (type)
           {
               case ClassType.TypeOdd
                   Map(m => m.Field1);
                   Map(m => m.Field3);
                   Map(m => m.Field5);                 
                   break;
               case ClassType.TypeEven:
                   Map(m => m.Field2);
                   Map(m => m.Field4);
                   Map(m => m.Field6);                 
                   break;
               case ClassType.TypeAll:
                   Map(m => m.Field1);
                   Map(m => m.Field2);
                   Map(m => m.Field3);
                   Map(m => m.Field4);
                   Map(m => m.Field5);
                   Map(m => m.Field6);                 
                   break;
           }
       }
   }
   

2. Write out the records to using the mapping configuration

   using (var memoryStream = new MemoryStream())
   using (var streamWriter = new StreamWriter(memoryStream))
   using (var csvWriter = new CsvWriter(streamWriter))
   {
       csvWriter.Configuration.RegisterClassMap(new MyClassMap(ClassType.TypeOdd));
       csvWriter.WriteRecords(records);
       streamWriter.Flush();
       return memoryStream.ToArray();
   }
   

Mark the field like this:

[CsvField( Ignore = true )]
public double ResultQuantity { get; private set; }

Update: Nevermind. I see you want to do this at runtime, rather than compile time. I'll leave this up as red flag for anyone else who might make the same mistake.

You can do this:

using (var myStream = saveFileDialog1.OpenFile())
{
    using (var writer = new CsvWriter(new StreamWriter(myStream)))
    {
        writer.Configuration.AttributeMapping(typeof(DataView)); // Creates the CSV property mapping
        writer.Configuration.Properties.RemoveAt(1); // Removes the property at the position 1
        writer.Configuration.Delimiter = "\t";
        writer.WriteHeader(typeof(DataView));
        _researchResults.ForEach(writer.WriteRecord);
    }
}

We are forcing the creation of the attribute mapping and then modifying it, removing the column dynamically.