ASP.NET StreamWriter - new line after x commas

Question

Hey guys,

I've got a JS array which is writing to a text file on the server using StreamWriter. This is the line that does it:

sw.WriteLine(Request.Form["seatsArray"]);

At the moment one line is being written out with the entire contents of the array on it. I want a new line to be written after every 5 commas. Example array:

BN,ST,A1,303,601,BN,ST,A2,303,621,BN,WC,A3,303,641,

Should output:

BN,ST,A1,303,601,
BN,ST,A2,303,621,
BN,WC,A3,303,641,

I know I could use a string replace but I only know how to make this output a new line after every comma, and not after a specified amount of commas.

How can I get this to happen?

Thanks!

Answer 1

Well, here's the simplest answer I can think of:

string[] bits = Request.Form["seatsArray"].Split(',');

for (int i = 0; i < bits.Length; i++)
{
    sw.Write(bits[i]);
    sw.Write(",");
    if (i % 5 == 4)
    {
        sw.WriteLine();
    }
}

It's not terribly elegant, but it'll get the job done, I believe.

You may want this afterwards to finish off the current line, if necessary:

if (bits[i].Length % 5 != 0)
{
    sw.WriteLine();
}

I'm sure there are cleverer ways... but this is simple.

One question: are the values always three characters long? Because if so, you're basically just breaking the string up every 20 characters...

Answer 2

Something like:

var input = "BN,ST,A1,303,601,BN,ST,A2,303,621,BN,WC,A3,303,641,";
var splitted = input.Split(',');

var cols = 5;
var rows = splitted.Length / cols;

var arr = new string[rows, cols];

for (int row = 0; row < rows; row++)
    for (int col = 0; col < cols; col++)
        arr[row, col] = splitted[row * cols + col];

I will try find a more elegant solution. Properly with some functional-style over it.

Update: Just find out it is not actually what you needs. With this you get a 2D array with 3 rows and 5 columns.

This however will give you 3 lines. They do not have a ending ','. Do you want that? Do you always want to print it out? Or do you want to have access to the different lines?:

var splitted = input.Split(new [] { ','}, StringSplitOptions.RemoveEmptyEntries); 

var lines = from item in splitted.Select((part, i) => new { part, i })
            group item by item.i / 5 into g
            select string.Join(",", g.Select(a => a.part));

Or by this rather large code. But I have often needed a "Chunk" method so it may be reusable. I do not know whether there is a build-in "Chunk" method - couldn't find it.

public static class LinqExtensions
{
    public static IEnumerable<IList<T>> Chunks<T>(this IEnumerable<T> xs, int size)
    {
        int i = 0;

        var curr = new List<T>();

        foreach (var x in xs)
        {
            curr.Add(x);

            if (++i % size == 0)
            {
                yield return curr;
                curr = new List<T>();
            }
        }
    }
}

Usage:

var lines = input.Split(',').Chunks(5).Select(list => string.Join(",", list));