Checking phone numbers for equivalence - regex

Question

What's the best way to check phone numbers in different formats for equivalence?
Different formats:
"[phone]"
"7083997222"
"708-399-7222"
"708399-7222"
"[phone]"
"[phone]"
Additional Difficulty: what if the phone number isn't prefaced by the country code?

Answer 1

You can't use a single regular expression. To get a canonical representation that can be compared:
Replace an initial + with your international call prefix. In many countries this is 00.
If number doesn't start with the prefix, add the prefix and the country code for your country.
Remove all non-digits.
This will be sufficient if you only have to deal with calls made from a single country, for example if you are developing something for internal use at a phone company. If you have to accept a wide range of inputs from different countries with various prefixes I suggest finding a well tested library to do this.

Answer 2

You can implement PhoneEqualityComparer class. If you deal only with US numbers, the following code will work:
sealed class PhoneEqualityComparer : IEqualityComparer<string>
{
public bool Equals(string x, string y)
{
return string.Equals(NormalizePhone(x), NormalizePhone(y));
}
public int GetHashCode(string obj)
{
return NormalizePhone(obj).GetHashCode();
}
private static string NormalizePhone(string phone)
{
if (phone.StartsWith("+1"))
phone = phone.Substring(2);
return Regex.Replace(phone, #"\D", string.Empty);
}
}
Sample usage:
string[] phones = new[] {
"[phone]",
"7083997222",
"708-399-7222",
"708399-7222",
"[phone]",
"[phone]"
};
string[] uniquePhones = phones.Distinct(new PhoneEqualityComparer()).ToArray();

Answer 3

Try this regex
\(?\d{3}\)?-? *\d{3}-? *-?\d{4}
Or:
^\+?(\d[\d-]+)?(\([\d-.]+\))?[\d-]+\d$
Regex Demo

Answer 4

This is a pretty neat regex that will replace:
any plus sign followed by one or more digits
any character that is not a digit or a line break character
with a blank string
string text = Regex.Replace( inputString, #"\+\d+|[^0-9\r\n]", "" , RegexOptions.None | RegexOptions.Multiline );
Input:
"[phone]"
"7083997222"
"708-399-7222"
"708399-7222"
"[phone]"
"[phone]"
Output:
7083997222
7083997222
7083997222
7083997222
7083997222
7083997222