LINQ Extension Methods Cheat Sheet

LINQ Extension Methods are great. Here's a cheat sheet of the common ones:

Filter

Takes a larger set down to a smaller set

First

• customers.First(c => c.LastName == "Anderson")
  The first customer with a last name of Anderson

Last

• customers.Last(c => c.LastName == "Anderson")
  The last customer with a last name of Anderson

Single

• customers.Single(c => c.Id == 456)
  The only customer with an ID of 456

Where

• customers.Where(c => c.Active == true)
  All customers that are Active

FirstOrDefault

• customers.FirstOrDefault(c => c.LastName == "Anderson")
  The first customer with a last name of Anderson or null if there isn't one

LastOrDefault

• customers.LastOrDefault(c => c.LastName == "Anderson")
  The last customer with a last name of Anderson or null if there isn't one

SingleOrDefault

• customers.SingleOrDefault(c => c.Id = 999)
  The only customer with an ID of 999 or null if there isn't one

Sort

Returns a copy of a set but in a different order

OrderBy

• customers.OrderBy(c => c.LastName)
  Returns the customers sorted alphabetically by last name

OrderByDescending

• customers.OrderByDescending(c => c.LastOrderDate)
  Returns the customers sorted by the date they last placed an order (most recent first)

ThenBy (must be done after OrderBy or OrderByDescending)

• customers.OrderBy(c => c.LastName).ThenBy(c => c.FirstName)
  Returns the customers sorted first by last name then by first name

ThenByDescending (must be done after OrderBy or OrderByDescending)

• customers.Order(c => c.Category).ThenByDescending(c => c.LastOrderDate)
  Returns the customers sorted first by category then by the date they last placed an order (most recent first)

Conditional

Answers a yes/no question based on a set

All

• customers.All(c => c.Active == true)
  Is every customer in the set active?

Any

• customers.Any(c => c.LastOrderDate > DateTime.Now.AddDays(-7))
  Did any customer in the set make an order in the past 7 days?

Projection

Transforms a set of objects in one form to a set of objects in another form

Select

• IEnumerable<string> names = customers.Select(c => c.FirstName)
  Select the first name of every customer (transform each Customer object to a string object)

Extension methods always return a COPY:

• IEnumerable<Customer> sorted = customers.OrderBy(c => c.LastName)