LINQ: When to use SingleOrDefault vs. FirstOrDefault() with filtering criteria

Question

Consider the IEnumerable extension methods SingleOrDefault() and FirstOrDefault()

MSDN documents that SingleOrDefault:

Answer 1

I queried Google for the usage of the different methods on GitHub. This is done by running a Google search query for each method and limiting the query to the github.com domain and the .cs file extension by using the query "site:github.com file:cs ..."

It seems that the First* methods are more commonly used than the Single* methods.

| Method               | Results |
|----------------------|---------|
| FirstAsync           |     315 |
| SingleAsync          |     166 |
| FirstOrDefaultAsync  |     357 |
| SingleOrDefaultAsync |     237 |
| FirstOrDefault       |   17400 |
| SingleOrDefault      |    2950 |