按字母顺序排列，Array.Sort() 效果不佳

Question

I have problem with alphabetical order. Array.Sort() doesn't work well in my case.

string str = "AaBbCc";
char[] arr = second.ToCharArray();
Array.Sort(arr);

// Output: ABCabc
// I need: AaBbCc

Any ideas?

Answer 1

You can achieve what you're looking for with LINQ.

First, we need to break your characters up into a sequence of single character strings. We can do that with select.

str.Select(x => x.ToString())

Okay, now we want to order this list. The default sort for strings is word sort, which would order it like aAbBcC . Since you want to get the capitals first, we'll use the OrdinalIgnoreCase comparer, which will group our characters up.

   .OrderBy(x => x, StringComparer.OrdinalIgnoreCase)

Okay, so we've now grouped our characters. We'll now want to sort those groups ordinally to get the capitals to come first, using ThenBy.

   .ThenBy(x => x, StringComparer.Ordinal)

Finally, we can turn it into an array.

   .ToArray();

Bringing it together, we get the following:

var res = str.Select(x => x.ToString())
             .OrderBy(x => x, StringComparer.OrdinalIgnoreCase)
             .ThenBy(x => x, StringComparer.Ordinal)
             .ToArray();

Which gives us an array that looks like this: ["A","a","B","b","C","c"]

At this point, as @dvo has pointed out, we can turn it back into a single string with a call to String.Join, like so:

var resStr = string.Join("", res);

As @RufusL points out, we can do more for this query. Since we know we ultimately want a string, we can skip the ToArray call entirely and stick with the IOrderedEnumerable<string> .

var res = str.Select(x => x.ToString())
             .OrderBy(x => x, StringComparer.OrdinalIgnoreCase)
             .ThenBy(x => x, StringComparer.Ordinal);

Since we aren't joining anything with strings we can use string.Concat instead of string.Join .

var resStr = string.Concat(res);

Answer 2

The problem is that your code is ordering by the ASCII value, which is 65-90 for uppercase ( AZ ) and 97-122 for lowercase ( az ).

Asuming you always want the uppercase letters to come before their lowercase counterparts, we can use a little trick to sort the lowercase letters just after their uppercase value by subtracting 31.5 from the ASCII value before doing the comparison.

By doing this, a becomes 65.5 ( 97 - 31.5 ) and will be sorted between A ( 65 ) and B ( 66 ). Likewise for all the other lower-case letters. This avoids the cost of creating a bunch of new strings for comparison and doing multiple orderings.

For example:

string str = "zZYyabCABcxX";
string ordered = string.Concat(str.OrderBy(c => c > 96 && c < 123 ? c - 31.5 : c));
Console.WriteLine(ordered);

We can also use char.IsUpper and char.ToLower instead of hard-coded ascii values:

// If the character is lower-case, use the value of its upper-case counterpart plus .5
ordered = string.Concat(str.OrderBy(c => char.IsLower(c) ? char.ToUpper(c) + .5 : c));

Output:

---

Edit

To answer one of the comments, if you want to use this same method to sort the characters such that the lower-case letters come before their upper-case counterparts, you would then subtract 32.5 if the character is in the upper-case range. This way an a ( 97 ) becomes 64.5 ( 97 - 32.5 ) and will be sorted before A ( 65 ):

string ordered = string.Concat(str.OrderBy(c => c > 96 && c < 123 ? c - 32.5 : c));

Or using the trick with char.IsLower and char.ToUpper instead of hard-coded ascii values:

// If the character is lower-case, use the value of its upper-case counterpart minus .5
ordered = string.Concat(str.OrderBy(c => char.IsLower(c) ? char.ToUpper(c) - .5 : c));

Answer 3

There's also a solution that doesn't require doing math with the ASCII values: we can first order the characters so that the upper and lower case of each character are next to each other by using OrderBy(char.ToLower) (which sorts by the ASCII value of the character in lower case), and then we can sort them by char.IsLower , which will then sort the lower case characters after the upper case characters:

string str = "zZYyabCABcxX";
string ordered = string.Concat(str.OrderBy(char.ToLower).ThenBy(char.IsLower));

// ordered == "AaBbCcXxYyZz"