Generate CSV file from string[][]

Question

I have a MVC controller that should return a CSV file from a string[][] . I'm trying this example:

public FileContentResult DownloadCSV()
{
    string[][] output = new string[][]{  
            new string[]{"Col 1 Row 1", "Col 2 Row 1", "Col 3 Row 1"},  
            new string[]{"Col1 Row 2", "Col2 Row 2", "Col3 Row 2"}  
        };
    return File(output, "text/csv", "Report123.csv");
}

But I don't know how to create the file. How can I create a CSV file from string[][] ?

Answer 1

Here is a sample using LINQ.

public FileContentResult DownloadCSV()
{
    string[][] output = new string[][]{  
        new string[]{"Col 1 Row 1", "Col 2 Row 1", "Col 3 Row 1"},  
        new string[]{"Col1 Row 2", "Col2 Row 2", "Col3 Row 2"}  
    };

    var result = lines.Select(l=>string.Join(",", l))
                      .Aggregate(new StringBuilder(), (sb, v) => sb.AppendLine(v))
                      .ToString();

    return File(result, "text/csv", "Report123.csv");
}

... as an extension method ...

public static class ToolsEx
{
    public static string ToCsvString(this string[][] lines)
    {
        var query = lines.Select(l=>string.Join(",", l));
        var result = query.Aggregate(new StringBuilder(), (sb, v) => sb.AppendLine(v));
        return result.ToString();
    }
}

... after remembering that string.Join uses StringBuilder internal you could reduce this further to just be (this might be a bit much if someone else is going to maintain this after you) ...

public static string ToCsvString(this string[][] rows)
{
    return string.Join(Environment.NewLine, rows.Select(row => string.Join(",", row)));
}

Answer 2

Use an extension method to generate the csv file

    /// <summary>
    /// Convert an array to string list, of the form "1,2,3,.."        
    /// </summary>
    /// <param name="array">The array of numbers</param>
    /// <returns>A string value</returns>
    public static string ToCSVRow<T>(this T[] array)
    {
        string[] parts=new string[array.Length];
        for(int i=0; i<parts.Length; i++)
        {
            parts[i]=array[i].ToString();
        }
        return string.Join(",", parts);
    }
    /// <summary>
    /// Convert a jagged array to csv table, where each row has the form "1,2,3,.."
    /// </summary>
    /// <param name="array">The array of numbers</param>
    /// <returns>A string value</returns>
    public static string ToCSV<T>(this T[][] array)
    {
        List<string> csv=new List<string>();
        for(int i=0; i<array.Length; i++)
        {
            csv.Add(array[i].ToCSVRow());
        }
        return string.Join(Environment.NewLine, csv.ToArray());
    }

and use with

return File(output.ToCSV(), "text/csv", "Report123.csv");

Edit 1

Based on the comments it would be simpler and maybe faster to do the following:

    /// <summary>
    /// Convert an array to a csv row, of the form "1,2,3,4.."
    /// </summary>
    /// <typeparam name="T">The array type</typeparam>
    /// <param name="list">The array</param>
    /// <returns>A comma delimited string</returns>
    public static string ToCSVRow<T>(this T[] list)
    {
        return string.Join(",", list);
    }

    /// <summary>
    /// Convert a jagged array to csv table, where each row has the form "1,2,3,.."
    /// </summary>
    /// <param name="array">The array of numbers</param>
    /// <returns>A string value</returns>
    public static string ToCSV<T>(this T[][] array)
    {
        return string.Join(Environment.NewLine, array.Select((row) => string.Join(",", row)));
    }