.NET 9: Introducing LINQ Enhancements
Tags: dotnet, dotnetcore, linq, beginners
Published: 2024-03-11 11:27:04

### Streamlining Data Workflows with LINQ Enhancements

In the latest release of .NET 9, several enhancements have been introduced to LINQ, providing developers with more powerful and efficient ways to work with data. Among these enhancements are two new methods: CountBy and AggregateBy, along with the introduction of the Index<TSource> method. Let’s explore each of these additions in detail.

### CountBy Method:

The CountBy method offers a convenient way to calculate the frequency of each key in a collection without the need for intermediate groupings via GroupBy. This method is particularly useful when working with data where key frequencies need to be determined efficiently.

Consider the following example, where we aim to find the most frequently occurring word in a given text string:

    string sourceText = @"
        Lorem ipsum dolor sit amet, consectetur adipiscing elit.
        Sed non risus. Suspendisse lectus tortor, dignissim sit amet, 
        adipiscing nec, ultricies sed, dolor. Cras elementum ultrices amet diam.
    ";
    
    // Find the most frequent word in the text.
    KeyValuePair<string, int> mostFrequentWord = sourceText
        .Split(new char[] { ' ', '.', ',' }, StringSplitOptions.RemoveEmptyEntries)
        .Select(word => word.ToLowerInvariant())
        .CountBy(word => word)
        .MaxBy(pair => pair.Value);
    Console.WriteLine(mostFrequentWord.Key); // Output: amet

### AggregateBy Method:

The AggregateBy method enables developers to implement more general-purpose workflows for aggregating state by key. This method is particularly useful for scenarios where complex calculations or transformations are required based on key associations.

Take, for instance, the following example, where we calculate scores associated with specific keys:

    (string id, int score)[] data =
    {
        ("0", 42),
        ("1", 5),
        ("2", 4),
        ("1", 10),
        ("0", 25),
    };
    
    var aggregatedData = data.AggregateBy(
        keySelector: entry => entry.id,
        seed: 0,
        (totalScore, curr) => totalScore + curr.score
    );
    foreach (var item in aggregatedData)
    {
        Console.WriteLine(item);
    }
    // Output:
    // (0, 67)
    // (1, 15)
    // (2, 4)

### Index<TSource> Method:

The Index<TSource> method allows developers to quickly extract the implicit index of an enumerable. This feature simplifies scenarios where the index of items within a collection needs to be accessed or manipulated.

Consider the following example, where we automatically index items in a collection of lines read from a file:

    IEnumerable<string> lines = File.ReadAllLines("output.txt");
    foreach ((int index, string line) in lines.Index())
    {
        Console.WriteLine($"Line number: {index + 1}, Line: {line}");
    }

In summary, the latest enhancements to LINQ in .NET 9 provide developers with powerful tools for efficiently working with data. Whether calculating key frequencies, implementing custom aggregations, or indexing collections, these additions empower developers to write cleaner, more expressive code.

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