Fastest way to convert a list of objects to csv with each object values in a new line

Use servicestack.text

Install-Package ServiceStack.Text

and then use the string extension methods ToCsv(T)/FromCsv()

Examples: https://github.com/ServiceStack/ServiceStack.Text

Update: Servicestack.Text is now free also in v4 which used to be commercial. No need to specify the version anymore! Happy serializing!

Because speed was mentioned in the question, my interest was piqued on just what the relative performances might be, and just how fast I could get it.

I know that StringBuilder was excluded, but it still felt like probably the fastest, and StreamWriter has of course the advantage of writing to either a MemoryStream or directly to a file, which makes it versatile.

So I knocked up a quick test.

I built a list half a million objects identical to yours.

Then I serialized with CsvSerializer, and with two hand-rolled tight versions, one using a StreamWriter to a MemoryStream and the other using a StringBuilder.

The hand rolled code was coded to cope with quotes but nothing more sophisticated. This code was pretty tight with the minimum I could manage of intermediate strings, no concatenation... but not production and certainly no points for style or flexibility.

But the output was identical in all three methods.

The timings were interesting:

Serializing half a million objects, five runs with each method, all times to the nearest whole mS:

StringBuilder     703     734     828     671     718   Avge=     730.8
MemoryStream      812     937     874     890     906   Avge=     883.8
CsvSerializer   1,734   1,469   1,719   1,593   1,578   Avge=   1,618.6

This was on a high end i7 with plenty of RAM.

Other things being equal, I would always use the library.

But if a 2:1 performance difference became critical, or if RAM or other issues turned out to exaggerate the difference on a larger dataset, or if the data were arriving in chunks and was to be sent straight to disk, I might just be tempted...

Just in case anyone's interested, the core of the code (for the StringBuilder version) was

    private void writeProperty(StringBuilder sb, string value, bool first, bool last)
    {
        if (! value.Contains('\"'))
        {
            if (!first)
                sb.Append(',');

            sb.Append(value);

            if (last)
                sb.AppendLine();
        }
        else
        {
            if (!first)
                sb.Append(",\"");
            else
                sb.Append('\"');

            sb.Append(value.Replace("\"", "\"\""));

            if (last)
                sb.AppendLine("\"");
            else
                sb.Append('\"');
        }
    }

    private void writeItem(StringBuilder sb, Test item)
    {
        writeProperty(sb, item.Id.ToString(), true, false);
        writeProperty(sb, item.Name, false, false);
        writeProperty(sb, item.CreatedDate, false, false);
        writeProperty(sb, item.DueDate, false, false);
        writeProperty(sb, item.ReferenceNo, false, false);
        writeProperty(sb, item.Parent, false, true);
    }

Your best option would be to use an existing library. It saves you the hassle of figuring it out yourself and it will probably deal with escaping special characters, adding header lines etc. You could use the CSVSerializer from ServiceStack. But there are several other in nuget. Creating the CSV will then be as easy as string csv = CsvSerializer.SerializeToCsv(testobjs);