Counting number of occurrences of characters from array in string?

Question

I'm writing code to determine whether a password contains enough punctuation characters.

How do I count the number of occurrences of any characters from a set?

Something along these lines:

private const string nonAlphaNumericCharSet = "#*!?£$+-^<>[]~()&";
...
public static bool PasswordMeetsStrengthRequirements(string password)
{
    return password.Length >= MINIMUM_PASSWORD_LENGTH && password.NumberOfOccurences(nonAlphaNumericCharSet.ToCharArray()) >= MINIMUM_NONALPHANUMERIC_CHARS;
}

Bonus points for an elegant linq solution.

@Oliver: I guess Black Knight will be awarding a bounty (after the 24 hour wait period). — Chris Sinclair
– Chris Sinclair, Commented May 22, 2013 at 9:57
I was thinking about awarding upvotes. And of course my own personal gratitude ;). However, if people think an answer deserves a bounty then I'll award one. — Kev
– Kev, Commented May 22, 2013 at 9:58
Maybe this will help stackoverflow.com/questions/11569951/… — Liviu
– Liviu, Commented May 22, 2013 at 10:07

I4V · Accepted Answer · 2013-05-22 09:51:56Z

17

How do I count the number of occurences of any characters from a set?

var count = password.Count(nonAlphaNumericCharSet.Contains);

answered May 22, 2013 at 9:51

I4V

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4 Comments

Habib Over a year ago

+1, slick ..........., for those like me, its simpler form would be: var temp = password.Count(r=> nonAlphaNumericCharSet.Contains(r));

Kev Over a year ago

Thanks for the explanation. I was just wondering what the simpler form would be.

Habib Over a year ago

@Carra, yes by just 6 minutes.

Carra Over a year ago

That and it's also more efficient :)

Mogli · Accepted Answer · 2013-05-22 09:51:48Z

1

you can count like this

int count = "he!l!l!o".Split('!').Length - 1;

it will return 3.

Using linq

int count="he!l!l!o".Count(x => x == '!');

answered May 22, 2013 at 9:51

Mogli

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Comments

Carra · Accepted Answer · 2013-05-22 09:58:32Z

1

Here's an example:

private const string nonAlphaNumericCharSet = "#*!?£$+-^<>[]~()&";

public static bool PasswordMeetsStrengthRequirements(string password)
{
    return password.Count(x => nonAlphaNumericCharSet.Contains(x)) > 2 && password.Length > 1;
}

public static void Main()
{
    PasswordMeetsStrengthRequirements("Test").Dump();
    PasswordMeetsStrengthRequirements("Test#").Dump();
    PasswordMeetsStrengthRequirements("(Test#").Dump();
    PasswordMeetsStrengthRequirements("(Te[st#").Dump();
}

answered May 22, 2013 at 9:58

Carra

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Comments

giammin · Accepted Answer · 2013-05-22 12:35:18Z

1

what about a RegExp

Regex rgx = new Regex(@"^(?=.*(\W.*){4,}).{8,}$", RegexOptions.Compiled);
bool validPassword = rgx.IsMatch(password);

4=min not word/digit char

8= min password leght

Linq may be considered elegant (it isn't IMHO) but at which performance cost?

------------Update after comment---------------

if you want to match a subset of chars you have to replace \W with []

[]= range of chars

some chars have to be escaped with \

in your case: [#\*!\?£\$\+-\^\<\>\[\]~&]

there you can find a regular expression cheat sheet

edited May 22, 2013 at 12:35

answered May 22, 2013 at 10:37

giammin

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2 Comments

Kev Over a year ago

Thanks. Regexs are powerful but I'm not very good at them. It's important in this case however, to only match punctuation from a predefined set, not just all punctuation. How would I do that with a regex?

giammin Over a year ago

@BlackKnight just updated my answer. I'm not good at regular expression either. I find very usefull this cheatsheet: github.com/shadowbq/Cheat-Sheets/blob/master/regex/… i have printed it and it is always near my desk!

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