Chapter 7, LINQ Performance

1. Use the index rather than the Last() call for direct access to the last element in a collection. Avoid using the let keyword in your LINQ queries. Convert a list to an array to perform group by, and then return an enumerator.
2. The compiler generates more lines of code that take longer to run, and more memory is allocated at runtime than when the let keyword is not used.
3. Filter items starting with objects that have the least number of items, followed by the objects with an increasing number of items. Also, avoid using the let keyword.
4. Closures with parameters perform better than closures without parameters.