How Can LINQ Improve Line-by-Line File Reading in C#?

Reading Files Line by Line in C# with LINQ

When working with text files, it is often necessary to process each line individually. C# provides several ways to achieve this, including using a StreamReader and reading each line manually.

However, for improved efficiency and readability, LINQ (Language INtegrated Query) can be leveraged without compromising performance. LINQ offers a more concise and expressive syntax for working with data.

Consider two example scenarios where line-by-line reading is needed:

First Example:

using (var file = System.IO.File.OpenText(_LstFilename))
{
    while (!file.EndOfStream)
    {
        String line = file.ReadLine();

        // Process line
    }
}

Second Example:

using (var file = System.IO.File.OpenText(datFile))
{
    Regex nameRegex = new Regex("IDENTIFY (.*)");

    while (!file.EndOfStream)
    {
        String line = file.ReadLine();

        // Process line
    }
}

LINQ-based Approach:

To read files line by line with LINQ, we can use an iterator block to define a custom Enumerable sequence:

static IEnumerable<string> ReadFrom(string file)
{
    string line;
    using (var reader = File.OpenText(file))
    {
        while ((line = reader.ReadLine()) != null)
        {
            yield return line;
        }
    }
}

This method returns an IEnumerable object that lazily evaluates each line as it is requested, without buffering the entire file in memory.

We can then use LINQ queries to process the lines:

var lines = ReadFrom(path);

// Process lines using LINQ

With LINQ, we can apply filtering, ordering, and other operations to the line sequence, making code more efficient and readable. Note that if operations like OrderBy or GroupBy are used, LINQ may need to buffer the data, potentially affecting performance.

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