How to get latest files in C# - c#-3.0

Question

I have some files with same name but with different dates.
Basically we are finding the files with most recent dates
The file patterns are
<FileNames><YYYYMMDD><FileExtension>
e.g. test_20100506.xls indicates
<FileNames> = test_
<YYYYMMDD> = 20100506
<FileExtension> = .xls
Now in the source folder, the files are
standardization_20100503.xls,
standardization_20100504.xls,
standardization_20100305.xls,
replacement_20100505.xls
As can be seen that, standardization_.xls are 3 in numbers but
replacement_.xls is only 1.
The output will be a list of file names whose content will be
standardization_20100504.xls and replacement_20100505.xls
Because among all the standardization_.xls is the most recent one and replacement_.xls is also the same.
I have tried with my own logic but somehow failed.
My idea is as under
private static void GetLatestFiles(ref List<FileInfo> validFiles)
{
List<FileInfo> validFilesTemp = new List<FileInfo>();
for (int i = 0; i < validFiles.Count; i++)
{
for (int j = i+1; j < validFiles.Count; j++)
{
string getFileTextX = ExtractText(validFiles[i].Name);
string getFileTextY = ExtractText(validFiles[j].Name);
if (getFileTextX == getFileTextY)
{
int getFileDatesX = Convert.ToInt32(ExtractNumbers(validFiles[i].Name));
int getFileDatesY = Convert.ToInt32(ExtractNumbers(validFiles[j].Name));
if (getFileDatesX > getFileDatesY)
{
validFilesTemp.Add(validFiles[i]);
}
else
{
validFilesTemp.Add(validFiles[j]);
}
}
}
}
validFiles.Clear();
validFiles = validFilesTemp;
}
The ExtractNumbers is:
public static string ExtractNumbers(string expr)
{
return string.Join(null, System.Text.RegularExpressions.Regex.Split(expr, "[^\\d]"));
}
and the ExtractText is
public static string ExtractText(string expr)
{
return string.Join(null, System.Text.RegularExpressions.Regex.Split(expr, "[\\d]"));
}
I am using c#3.0 and framework 3.5

Answer 1

Use this regex to Get the date out of the full file name.
#"_([0-9]*)\."
Then Convert it to DateTime if you want as
DateTime dt;
dt = new DateTime();
dt = DateTime.ParseExact(MyString, "yyyyMMdd",null);
Use dt.CompareTo(dt1).Equals(1) to compare if the date is earlier or later.

Answer 2

class Program
{
static void Main()
{
var files =
from file in Directory.GetFiles(#"c:\somedirectory")
let name = Path.GetFileNameWithoutExtension(file)
let tokens = name.Split('_')
where tokens.Length > 1
let date = DateTime.ParseExact(tokens[1], "yyyyMMdd", CultureInfo.InvariantCulture)
orderby date descending
select file;
foreach (var item in files)
{
Console.WriteLine(item);
}
}
}