Keep only numeric value from a string?

问题

I have some strings like this

string phoneNumber = "(914) 395-1430";

I would like to strip out the parethenses and the dash, in other word just keep the numeric values.

So the output could look like this

9143951430

How do I get the desired output ?

回答1:

You do any of the following:

Use regular expressions. You can use a regular expression with either

A negative character class that defines the characters that are what you don't want (those characters other than decimal digits):

private static readonly Regex rxNonDigits = new Regex( @"[^\d]+");

In which case, you can do take either of these approaches:

// simply replace the offending substrings with an empty string
private string CleanStringOfNonDigits_V1( string s )
{
  if ( string.IsNullOrEmpty(s) ) return s ;
  string cleaned = rxNonDigits.Replace(s, "") ;
  return cleaned ;
}

// split the string into an array of good substrings
// using the bad substrings as the delimiter. Then use
// String.Join() to splice things back together.
private string CleanStringOfNonDigits_V2( string s )
{
  if (string.IsNullOrEmpty(s)) return s;
  string cleaned = String.Join( rxNonDigits.Split(s) );
  return cleaned ;
}

a positive character set that defines what you do want (decimal digits):

private static Regex rxDigits = new Regex( @"[\d]+") ;

In which case you can do something like this:

private string CleanStringOfNonDigits_V3( string s )
{
  if ( string.IsNullOrEmpty(s) ) return s ;
  StringBuilder sb = new StringBuilder() ;
  for ( Match m = rxDigits.Match(s) ; m.Success ; m = m.NextMatch() )
  {
    sb.Append(m.Value) ;
  }
  string cleaned = sb.ToString() ;
  return cleaned ;
}

You're not required to use a regular expression, either.

You could use LINQ directly, since a string is an IEnumerable<char>:

private string CleanStringOfNonDigits_V4( string s )
{
  if ( string.IsNullOrEmpty(s) ) return s;
  string cleaned = new string( s.Where( char.IsDigit ).ToArray() ) ;
  return cleaned;
}

If you're only dealing with western alphabets where the only decimal digits you'll see are ASCII, skipping char.IsDigit will likely buy you a little performance:

private string CleanStringOfNonDigits_V5( string s )
{
  if (string.IsNullOrEmpty(s)) return s;
  string cleaned = new string(s.Where( c => c-'0' < 10 ).ToArray() ) ;
  return cleaned;
}

Finally, you can simply iterate over the string, chucking the digits you don't want, like this:

private string CleanStringOfNonDigits_V6( string s )
{
  if (string.IsNullOrEmpty(s)) return s;
  StringBuilder sb = new StringBuilder(s.Length) ;
  for (int i = 0; i < s.Length; ++i)
  {
    char c = s[i];
    if ( c < '0' ) continue ;
    if ( c > '9' ) continue ;
    sb.Append(s[i]);
  }
  string cleaned = sb.ToString();
  return cleaned;
}

Or this:

private string CleanStringOfNonDigits_V7(string s)
{
  if (string.IsNullOrEmpty(s)) return s;
  StringBuilder sb = new StringBuilder(s);
  int j = 0 ;
  int i = 0 ;
  while ( i < sb.Length )
  {
    bool isDigit = char.IsDigit( sb[i] ) ;
    if ( isDigit )
    {
      sb[j++] = sb[i++];
    }
    else
    {
      ++i ;
    }
  }
  sb.Length = j;
  string cleaned = sb.ToString();
  return cleaned;
}

From a standpoint of clarity and cleanness of code, the version 1 is what you want. It's hard to beat a one liner.

If performance matters, my suspicion is that the version 7, the last version, is the winner. It creates one temporary — a StringBuilder() and does the transformation in-place within the StringBuilder's in-place buffer.

The other options all do more work.

回答2:

use reg expression

 string result = Regex.Replace(phoneNumber, @"[^\d]", "");

回答3:

try something like this

  return new String(input.Where(Char.IsDigit).ToArray());

回答4:

string phoneNumber = "(914) 395-1430";
var numbers = String.Join("", phoneNumber.Where(char.IsDigit));

回答5:

He means everything @gleng

Regex rgx = new Regex(@"\D");
str = rgx.Replace(str, "");

回答6:

Instead of a regular expression, you can use a LINQ method:

phoneNumber = String.Concat(phoneNumber.Where(c => c >= '0' && c <= '9'));

or:

phoneNumber = String.Concat(phoneNumber.Where(Char.IsDigit));

来源：https://stackoverflow.com/questions/19167669/keep-only-numeric-value-from-a-string

标签

regex

string

numeric