There are many situations where you need to read data from a file into memory or a database. Lets consider this scenario.

We have a tab delimited data file that has been exported from some web or windows application etc. Below is the sample file.

carrots    4    0.64
beans      3    0.12
oranges    7    1.02
apples     5    0.87

This file includes three columns. Column 1is the name of the product. Column 2 is the quantity and Column 3 is the unit price. We would also like a total price column derived from column 2 being multiplied by column 3.

Our aim here is to load these into our application programmatically and then bind them to a gridview. Normally you would have to read the file in line by line then do a split on each line, enter each line into a prebuilt class or datatable then add a new column and multiply the quantity by the price to obtain the total. However by using a nice little extension helper method, all of this can be rolled into just a few lines of code.

public static IEnumerable<string> ReadLinesFromFile(string filename)
{
    using (StreamReader reader = new StreamReader(filename))
    {
        while (true)
        {
            string s = reader.ReadLine();
            if (s == null)
                break;
            yield return s;
        }
    }
}

Above is the extension method to convert lines of a file into a IEnumerable list of strings.

var products = from line in ReadLinesFromFile(@"c:\import.txt")
               let item = line.Split('\t')
               select new
               {
                   Product = item[0],
                   Quantity = Convert.ToInt32(item[1]),
                   Price = Convert.ToDecimal(item[2]),
                   Total = Convert.ToInt32(item[1]) * Convert.ToDecimal(item[2])
               };

GridView1.DataSource = products;
GridView1.DataBind();

What this gives us is a list of products, with each one having 4 properties associated with it. We can then bind this straight to a gridview by setting the datasource of the gridview to products and calling the DataBind() method. This will display a table with 4 columns with the headers Product, Quantity, Price and Total.

The Linq statement can then be modified in many ways to accommodate different file formats (eg. CSV or fixed width) with a few simple changes.

This is just another way Linq is making things easier!

Schotime