Importing Data Files with Linq

.NET

In my previous Linq post I discussed using Linq with Regular expressions and how much less code was needed. In this post we’ll again see how Linq can be used to speed up and simplify development.

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