计算c＃中大写字符数的最快方法

Question

Any thoughts on the efficiency of this? ...

CommentText.ToCharArray().Where(c => c >= 'A' && c <= 'Z').Count()

Answer 1

Ok, just knocked up some code to time your method against this:

int count = 0;
for (int i = 0; i < s.Length; i++)
{
    if (char.IsUpper(s[i])) count++;
}

The result:

Yours: 19737 ticks

Mine: 118 ticks

Pretty big difference! Sometimes the most straight-forward way is the most efficient.

Edit

Just out of interest, this:

int count = s.Count(c => char.IsUpper(c));

Comes in at at around 2500 ticks. So for a "Linqy" one-liner it's pretty quick.

Answer 2

First there is no reason you need to call ToCharArray() since, assuming CommentText is a string it is already an IEnumerable<char> . Second, you should probably be calling char.IsUpper instead of assuming you are only dealing with ASCII values. The code should really look like,

CommentText.Count(char.IsUpper)

Third, if you are worried about speed there isn't much that can beat the old for loop,

int count = 0;
for (int i = 0; i < CommentText.Length; i++) 
   if (char.IsUpper(CommentText[i]) count++;

In general, calling any method is going to be slower than inlining the code but this kind of optimization should only be done if you are absolutely sure this is the bottle-neck in your code.

Answer 3

You're only counting standard ASCII and not ÃÐÊ etc.

How about

CommentText.ToCharArray().Where(c => Char.IsUpper(c)).Count()

Answer 4

Without even testing I'd say

int count = 0;
foreach (char c in commentText)
{
    if (Char.IsUpper(c))
        count++;
}

is faster, off now to test it.

Answer 5

What you are doing with that code is to create a collection with the characters, then create a new collection containing only the uppercase characters, then loop through that collection only to find out how many there are.

This will perform better (but still not quite as good as a plain loop), as it doesn't create the intermediate collections:

CommentText.Count(c => Char.IsUpper(c))

Edit: Removed the ToCharArray call also, as Matt suggested.

Answer 6

I've got this

Regex x = new Regex("[A-Z]{1}", 
  RegexOptions.Compiled | RegexOptions.CultureInvariant);
int c = x.Matches(s).Count;

but I don't know if its particularly quick. It won't get special chars either, I s'pose

EDIT:

Quick comparison to this question's answer. Debug in vshost, 10'000 iterations with the string:
aBcDeFGHi1287jKK6437628asghwHllmTbynerA

• The answer: 20-30 ms
• The regex solution: 140-170 ms