Generic List to CSV String

Question

I have a list that I want to write to a CSV string.

The examples I have found all seem to be for single item lists, mine has multiple items.

The code I currently have is;

private static string CreateCSVTextFile<T>(List<T> data, string seperator = ",") where T : ExcelReport, new()
{
  var objectType = typeof(T);
  var properties = objectType.GetProperties();
  var currentRow = 0;
  var returnString = "";
  foreach (var row in data)
  {
    var currentColumn = 0;
    var lineString = "";
    foreach (var info in properties)
    {
      lineString = lineString + info.GetValue(row, null) + seperator;
      currentColumn++;
    }
    if (seperator != "")
    {
      lineString = lineString.Substring(0, lineString.Count() - 2);
    }
    returnString = returnString + Environment.NewLine + lineString;
    currentRow++;
  }
  return returnString;
}

But when the list is large this method takes a very long time to run.

The class my list is based on looks like;

internal class ClientMasterFile
{
public String COL1{ get; set; }
public String COL2{ get; set; }
public String COL3{ get; set; }
public String COL4{ get; set; }
public String COL5{ get; set; }
public String COL6{ get; set; }
public String COL7{ get; set; }
public String COL8{ get; set; }
public String COL9{ get; set; }
public String COL10{ get; set; }
public String COL11{ get; set; }
public String COL12{ get; set; }
}

Is there a faster way to do this using an advanced version of String.Join?

Thanks

Answer 1

Your method can be simplified using StringBuilder and string.Join.

Concatenating strings directly is slow and uses a lot of memory which is fine for small operations.

See: Does StringBuilder use more memory than String concatenation?

private static string CreateCSVTextFile<T>(List<T> data, string seperator = ",")
{
    var properties = typeof(T).GetProperties();
    var result = new StringBuilder();

    foreach (var row in data)
    {
        var values = properties.Select(p => p.GetValue(row, null));
        var line = string.Join(seperator, values);
        result.AppendLine(line);
    }

    return result.ToString();
}

A more complete implementation for CSVs:

private static string CreateCSVTextFile<T>(List<T> data)
{
    var properties = typeof(T).GetProperties();
    var result = new StringBuilder();

    foreach (var row in data)
    {
        var values = properties.Select(p => p.GetValue(row, null))
                               .Select(v => StringToCSVCell(Convert.ToString(v)));
        var line = string.Join(",", values);
        result.AppendLine(line);
    }

    return result.ToString();
}

private static string StringToCSVCell(string str)
{
    bool mustQuote = (str.Contains(",") || str.Contains("\"") || str.Contains("\r") || str.Contains("\n"));
    if (mustQuote)
    {
        StringBuilder sb = new StringBuilder();
        sb.Append("\"");
        foreach (char nextChar in str)
        {
            sb.Append(nextChar);
            if (nextChar == '"')
                sb.Append("\"");
        }
        sb.Append("\"");
        return sb.ToString();
    }

    return str;
}

Using: escaping tricky string to CSV format