How to read .csv file into array using LINQ

I want to open the csv file and read each line into an index of an array using LINQ in C#.

So let's split it into three separate parts:

• Given a filename, open the file and read a sequence of lines
• given a sequence of lines, change it into a sequence of [index, line]
• given a sequence of [index, line] change it to the string format you want

And of course we want to do this all very LINQ-like, because we like LINQ (pun intended)

Let's do this writing extension functions. See Extension Methods Demystified

static class MyExtensionMethods
{
    // TODO add the extension methods
}

The first one: input a string fileName, output a sequence of lines (= strings)

public static IEnumerable<string> ReadLines(this string fileName)
{
    // TODO: check fileName not null, empty; check file exists
    FileInfo file = new FileInfo(fileName);
    using (TextReader reader = file.OpenText())
    {
        string line = reader.ReadLine();
        while (line != null)
        {
            yield return line;
            line = reader.ReadLine();
        }
    }

Convert a sequence of Lines into a sequence of [index, line]

IEnumerable<KeyValuePair<int, string>> ToIndexedLines(this IEnumerable<string> lines)
{
    return lines.Select( (line, index) => new KeyValuePair<int, string>(index, line));
}

And the third function: given a sequence of [index, line] convert it to a sequence of strings.

To make this re-usable I'll use a format string, so the caller can decide how to print his output. The format string has indexes {0} and {1}

IEnumerable<string> ToString(this IEnumerable<KeyValuePair<int, string>> indexLines,
   string formatString)
{
    // TODO: check input not null
    return indexLines.Select(keyValuePair =>
           String.Format(formatString, keyValuePair.Key, keyValuePair.Value);
}

After three one-liner functions we are able to read your file in a LINQ like fashion

const string fileName = "MyFile.Csv";
const string myFormatString = "{1} //array[{0}]";

IEnumerable<string> myRequestedOutput = fileName.ReadLines()
    .ToIndexedLines()
    .ToString(myFormatString);

Simple comme bonjour!