Difference Between Select and SelectMany

Question

I\'ve been searching the difference between Select and SelectMany but I haven\'t been able to find a suitable answer. I need to learn the differenc

Answer 1

SelectMany flattens queries that return lists of lists. For example

public class PhoneNumber
{
    public string Number { get; set; }
}

public class Person
{
    public IEnumerable PhoneNumbers { get; set; }
    public string Name { get; set; }
}

IEnumerable people = new List();

// Select gets a list of lists of phone numbers
IEnumerable> phoneLists = people.Select(p => p.PhoneNumbers);

// SelectMany flattens it to just a list of phone numbers.
IEnumerable phoneNumbers = people.SelectMany(p => p.PhoneNumbers);

// And to include data from the parent in the result: 
// pass an expression to the second parameter (resultSelector) in the overload:
var directory = people
   .SelectMany(p => p.PhoneNumbers,
               (parent, child) => new { parent.Name, child.Number });

Live Demo on .NET Fiddle