C# Regex for getting all possible matches

Question

I'd like to extract all the occurences of this regex

\d{7,8}

(every number that has 7 or 8 length)

The input cuould be something like

asd123456789bbaasd

what I want is an array with:

["1234567", "12345678", "2345678", "23456789"]

all the possible occurencies of a number that has 7 or 8 lenth.

Regex.Matches works diferent, it returns all the consecutive occurencies of matches.... ["12345678"]

Any idea?

Could you please include your [code](https://stackoverflow.com/help/mcve)? Makes it easier to give you an accurate and succinct answer — Fix, Sep 07 '18 at 19:36
regex is not designed for this. you have to do the permutation yourself — Steve, Sep 07 '18 at 19:37
You'd need to match on one digit and have the rest be in a look ahead. — juharr, Sep 07 '18 at 19:38
Something like [`(?=(\d{7}))(?=(\d{8})?)`](https://regex101.com/r/JQb0n8/1) — bobble bubble, Sep 07 '18 at 19:39
@elgonzo That won't work as it will miss numbers of 7 and 8 length starting from the same index. You would then need to seperate the regex to 2 steps. — Haytam, Sep 07 '18 at 19:42
@Haytam, yes you are right. Ooops! I delete my comment with that not quite fitting answer link... :-) — , Sep 07 '18 at 19:44

bobble bubble · Accepted Answer · 2018-09-07T20:36:51.360

5

For overlapping matches you'd need to capture inside a lookahead.

(?=(\d{7}))(?=(\d{8})?)

See this demo at regex101

(?=(\d{7})) the first capturing group is mandatory and will capture any 7 digits
(?=(\d{8})?) the second capturing group is optional (triggered at same position)

So if there are 7 digit matches, they will be in group(1) and if 8 digit matches, in group (2). In .NET Regex you can probably use one name for both groups.

For getting 7 digit matches only if there are 8 ahead, drop the ? after (\d{8}) like in this demo.

edited Sep 07 '18 at 20:36

answered Sep 07 '18 at 19:46

bobble bubble

16,888
3
27
46

Get all Group 1 and 2 values, remove empty ones and it will work as expected. – Wiktor Stribiżew Sep 07 '18 at 19:49
Amazing! that's what I needed – Rodrigo Fernández Sep 07 '18 at 20:38

blaze_125 · Answer 2 · 2018-09-07T20:04:38.837

Not really what you asked for, but the end result is.

using System;
using System.Collections.Generic;

namespace _52228638_ExtractAllPossibleMatches
{
    class Program
    {

        static void Main(string[] args)
        {
            string inputStr = "asd123456789bbaasd";
            foreach (string item in GetTheMatches(inputStr))
            {
                Console.WriteLine(item);
            }
            Console.ReadLine();
        }

        private static List<string> GetTheMatches(string inputStr)
        {
            List<string> retval = new List<string>();
            int[] lengths = new int[] { 7, 8 };
            for (int i = 0; i < lengths.Length; i++)
            {
                string tmp = new System.Text.RegularExpressions.Regex("(\\d{" + lengths[i] + ",})").Match(inputStr.ToString()).ToString();
                while (tmp.Length >= lengths[i])
                {
                    retval.Add(tmp.Substring(0, lengths[i]));
                    tmp = tmp.Remove(0, 1);
                }
            }
            return retval;
        }
    }
}

C# Regex for getting all possible matches

2 Answers2