Have you used SelectMany?

Yes, the SelectMany method in C# is used to project each element of a sequence into an IEnumerable and then flatten all of these sequences into a single, flat collection.

This is useful when you have a collection of collections and want to obtain a single combined collection of all elements.

Example:

var list = new List<List<int>> {
    new List<int> {1, 2, 3},
    new List<int> {4, 5},
    new List<int> {6}
};

var flatList = list.SelectMany(innerList => innerList);

foreach(var num in flatList)
{
    Console.WriteLine(num); // Will output numbers from 1 to 6 in order
}

SelectMany is often used for working with nested data structures, for example, to extract all elements from nested collections or to combine the results of multiple queries in LINQ.