LINQ grouping and ordering doesn't work as expected - linq

Question

My expected output is:
Extension: .txt -- CATS.TXT -- DOGS.TXT Extension: .pdf --
INFO.PDF -- TEST2.PDF Extension: .doc -- SUMMARY.DOC --
TEST1.DOC
Here are the functions.
public void TestGroupByFluentSyntax()
{
string[] files = new string[] { "test1.doc", "test2.pdf", "cats.txt", "dogs.txt", "info.pdf", "summary.doc" };
IEnumerable<IGrouping<string, string>> query = files.GroupBy(file => System.IO.Path.GetExtension(file), file => file.ToUpper())
.OrderBy(grouping => grouping.Key);
foreach(IGrouping<string, string> grouping in query)
{
Console.WriteLine("Extension: " + grouping.Key);
foreach (string fileName in grouping)
Console.WriteLine(" -- " + fileName);
}
}
public void TestGroupByFluentSyntax2()
{
string[] files = new string[] { "test1.doc", "test2.pdf", "cats.txt", "dogs.txt", "info.pdf", "summary.doc" };
IEnumerable<IGrouping<string, string>> query = files.OrderBy(file => file).GroupBy(file => System.IO.Path.GetExtension(file), file => file.ToUpper());
foreach (IGrouping<string, string> grouping in query)
{
Console.WriteLine("Extension: " + grouping.Key);
foreach (string fileName in grouping)
Console.WriteLine(" -- " + fileName);
}
}
If I order first, then group it works. But grouping & ordering doesn't. What am I missing on the function 'TestGroupByFluentSyntax()' where I group, then order?

Answer 1

You are not that far away. In TestGroupByFluentSyntax(), your output is:
Extension: .doc
-- TEST1.DOC
-- SUMMARY.DOC
Extension: .pdf
-- TEST2.PDF
-- INFO.PDF
Extension: .txt
-- CATS.TXT
-- DOGS.TXT
You group by the extension and sort on extension. So when you display, the extension is from doc, pdf and txt. But the file in each group is not sorted. You can achieve your desired output (by reversing the order of extension - use OrderByDescending as:
IEnumerable<IGrouping<string, string>> query
= files.GroupBy(file => System.IO.Path.GetExtension(file), file => file.ToUpper())
.OrderByDescending(grouping => grouping.Key);
And when you display (sort each group - use OrderBy), use:
foreach (string fileName in grouping.OrderBy(name => name))
Console.WriteLine(" -- " + fileName);
Here will be the output:
Extension: .txt
-- CATS.TXT
-- DOGS.TXT
Extension: .pdf
-- INFO.PDF
-- TEST2.PDF
Extension: .doc
-- SUMMARY.DOC
-- TEST1.DOC

Answer 2

This worked:
public void TestGroupByFluentSyntax()
{
Console.WriteLine("TestGroupByFluentSyntax");
string[] files = new string[] { "test1.doc", "test2.pdf", "cats.txt", "dogs.txt", "info.pdf", "summary.doc" };
IEnumerable<IGrouping<string, string>> query = files.GroupBy(file => System.IO.Path.GetExtension(file), file => file.ToUpper());
foreach (IGrouping<string, string> grouping in query)
{
Console.WriteLine("Extension: " + grouping.Key);
foreach (string fileName in grouping.OrderBy(name => name))
Console.WriteLine(" -- " + fileName);
}
}