R/W csv with dynamic size of columns to a lookup table by CSVHelper

Except for @dbc comment that the order of the items may change due to the unordered nature of Dictionary<TKey, TValue>, this should work.

void Main()
{
    var lookup_table = new Dictionary<string, Dictionary<string, string>>();
    
    using (var reader = new StringReader(",Header1,Header2,Header3\nKey1,value11,value12,value13\nKey2,value21,value22,value23"))
    using (var csv = new CsvReader(reader, CultureInfo.InvariantCulture))
    {       
        csv.Read();
        csv.ReadHeader();
        
        var headerLength = csv.Context.Reader.HeaderRecord.Length;
        var header = csv.Context.Reader.HeaderRecord;
        
        while (csv.Read())
        {
            var key = csv.GetField(0);
            lookup_table.Add(key, new Dictionary<string, string>());
            
            for (int i = 1; i < headerLength; i++)
            {
                lookup_table[key][header[i]] = csv.GetField(i);
            }
        }
    }
    
    using (var csv = new CsvWriter(Console.Out, CultureInfo.InvariantCulture))
    {
        var headers = lookup_table.First().Value.Keys.ToList();
        
        csv.WriteField(string.Empty);
        
        foreach (var header in headers)
        {
            csv.WriteField(header);
        }
        
        csv.NextRecord();
        
        foreach (KeyValuePair<string, Dictionary<string, string>> entry in lookup_table)
        {
            csv.WriteField(entry.Key);
            
            for (int i = 0; i < headers.Count; i++)
            {
                csv.WriteField(entry.Value[headers[i]]);
            }
            
            csv.NextRecord();
        }
    }
}