Question

I’m seeing some very strange sorting behaviour using CaseInsensitiveComparer.DefaultInvariant. Words that start with a leading hyphen “-” end up sorted as if the hyphen wasn’t there rather than being sorted in front of actual letters which is what happens with other punctuation.

So given { “hello”, “.net”, “-less”} I end up with {“.net”, “hello”, “-less” } instead of the expected {“-less”, “.net”, “hello”}.

Or, phrased as a test case:

[TestMethod]
public void TestMethod1()
{
    var rg = new String[] { 
        "x", "z", "y", "-less", ".net", "- more", "a", "b"
    };

    Array.Sort(rg, CaseInsensitiveComparer.DefaultInvariant);

    Assert.AreEqual(
        "- more,-less,.net,a,b,x,y,z", 
        String.Join(",", rg)
    );
}

… which fails like this:

Assert.AreEqual failed. 
Expected:<- more,-less,.net,a,b,x,y,z>. 
Actual:  <- more,.net,a,b,-less,x,y,z>.

Any ideas what’s going on?

Edit:

Looks like, by default .NET does fancy things when sorting strings which causes leading hyphens to be sorted into strange places so that co-op and coop sort together. Thus, if you want your leading hyphen words to end up and the begining with the other punctutation you have to tell it not not to:

Array.Sort(rg, (a, b) => String.CompareOrdinal(a, b));

Answer 1

Comparison procedures use the CultureInfo.InvariantCulture to determine the sort order and casing rules. String comparisons might have different results depending on the culture. For more information on culture-specific comparisons, see the System.Globalization namespace and Encoding and Localization.
From here.

The interesting part:

A word sort performs a culture-sensitive comparison of strings in which certain nonalphanumeric Unicode characters might have special weights assigned to them. For example, the hyphen (-) might have a very small weight assigned to it so that “coop” and “co-op” appear next to each other in a sorted list.
From here.