How Can LINQ Efficiently Read a File Line by Line in C#?

Reading a File Line by Line in C# Using LINQ

When dealing with text files in C#, it's essential to read each line efficiently. While using a StreamReader and iterating over lines individually is a common approach, exploring more efficient methods using LINQ is a worthwhile endeavor.

Efficient LINQ Implementation

To achieve this efficiency, a LINQ-based line reader can be implemented using an iterator block. This approach avoids loading the entire file into memory, ensuring operational efficiency for large files:

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

Enhanced LINQ Syntax for Readability

To enhance readability, an even more concise syntax can be employed:

static IEnumerable<string> ReadFrom(string file) {
    string line;
    using (var reader = File.OpenText(file)) {
        while ((line = reader.ReadLine()) != null) {
            yield return line;
        }
    }
}
...
var typedSequence = from line in ReadFrom(path)
                    let record = ParseLine(line)
                    where record.Active // for example
                    select record.Key;  

This version provides a lazily evaluated sequence without buffering, allowing subsequent operations like Where and OrderBy to be applied efficiently.

Additional Considerations

Note that using OrderBy or the standard GroupBy will buffer the data in memory. For grouping and aggregation tasks, PushLINQ offers specialized techniques to handle large datasets efficiently without incurring buffering penalties.

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