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Grouping

Context: GroupBy groups elements by a key. It returns a sequence of IGrouping<TKey, TElement>.

var people = new[]
{
    new { Name = "Alice", City = "Paris" },
    new { Name = "Bob", City = "London" },
    new { Name = "Charlie", City = "Paris" }
};

var grouped = people.GroupBy(p => p.City);
foreach (var group in grouped)
{
    Console.WriteLine(group.Key);
    foreach (var person in group)
        Console.WriteLine($"  {person.Name}");
}

Real-world usage example

Dashboard analytics: Group sales data by month, product category, or region.

Example: In EF Core, GroupBy translates to SQL GROUP BY.