What is the shortest way in .NET to sort strings starting with 1, 10 and 2 and respect the number ordering?

Question

I need to sort file names as follows: 1.log, 2.log, 10.log

But when I use OrderBy(fn => fn) it will sort them as: 1.log, 10.log, 2.log

I obviously know that this could be done by writing another comparer, but is there a simpler way to change from lexicographical order to natural sort order?

Edit: the objective is to obtain the same ordering as when selecting "order by name" in Windows Explorer.

Answer 1

You can use the Win32 CompareStringEx function. On Windows 7 it supports the sorting you need. You will have use P/Invoke:

static readonly Int32 NORM_IGNORECASE = 0x00000001;
static readonly Int32 NORM_IGNORENONSPACE = 0x00000002;
static readonly Int32 NORM_IGNORESYMBOLS = 0x00000004;
static readonly Int32 LINGUISTIC_IGNORECASE = 0x00000010;
static readonly Int32 LINGUISTIC_IGNOREDIACRITIC = 0x00000020;
static readonly Int32 NORM_IGNOREKANATYPE = 0x00010000;
static readonly Int32 NORM_IGNOREWIDTH = 0x00020000;
static readonly Int32 NORM_LINGUISTIC_CASING = 0x08000000;
static readonly Int32 SORT_STRINGSORT = 0x00001000;
static readonly Int32 SORT_DIGITSASNUMBERS = 0x00000008; 

static readonly String LOCALE_NAME_USER_DEFAULT = null;
static readonly String LOCALE_NAME_INVARIANT = String.Empty;
static readonly String LOCALE_NAME_SYSTEM_DEFAULT = "!sys-default-locale";

[DllImport("kernel32.dll", CharSet = CharSet.Unicode)]
static extern Int32 CompareStringEx(
  String localeName,
  Int32 flags,
  String str1,
  Int32 count1,
  String str2,
  Int32 count2,
  IntPtr versionInformation,
  IntPtr reserved,
  Int32 param
);

You can then create an IComparer that uses the SORT_DIGITSASNUMBERS flag:

class LexicographicalComparer : IComparer<String> {

  readonly String locale;

  public LexicographicalComparer() : this(CultureInfo.CurrentCulture) { }

  public LexicographicalComparer(CultureInfo cultureInfo) {
    if (cultureInfo.IsNeutralCulture)
      this.locale = LOCALE_NAME_INVARIANT;
    else
      this.locale = cultureInfo.Name;
  }

  public Int32 Compare(String x, String y) {
    // CompareStringEx return 1, 2, or 3. Subtract 2 to get the return value.
    return CompareStringEx( 
      this.locale, 
      SORT_DIGITSASNUMBERS, // Add other flags if required.
      x, 
      x.Length, 
      y, 
      y.Length, 
      IntPtr.Zero, 
      IntPtr.Zero, 
      0) - 2; 
  }

}

You can then use the IComparer in various sorting API's:

var names = new [] { "2.log", "10.log", "1.log" };
var sortedNames = names.OrderBy(s => s, new LexicographicalComparer());

You can also use StrCmpLogicalW which is the function used by Windows Explorer. It has been available since Windows XP:

[DllImport("shlwapi.dll", CharSet = CharSet.Unicode)]
static extern Int32 StrCmpLogical(String x, String y);

class LexicographicalComparer : IComparer<String> {

  public Int32 Compare(String x, String y) {
    return StrCmpLogical(x, y);
  }

}

Simpler, but you have less control over the comparison.