Finding the longest substring regex?

Question

Someone knows how to find the longest substring composed of letters using using MatchCollection.

public static Regex pattern2 = new Regex("[a-zA-Z]");
public static string zad3 = "ala123alama234ijeszczepsa";

Answer 1

You can loop over all matches and get the longest:

string max = "";

foreach (Match match in Regex.Matches(zad3, "[a-zA-Z]+"))
    if (max.Length < match.Value.Length)
        max = match.Value;

Answer 2

Try this:

 MatchCollection matches = pattern2.Matches(txt);
 List<string> strLst = new List<string>();
 foreach (Match match in matches)
     strLst.Add(match.Value);
 var maxStr1 = strLst.OrderByDescending(s => s.Length).First();

or better way :

 var maxStr2 = matches.Cast<Match>().Select(m => m.Value).ToArray().OrderByDescending(s => s.Length).First();

Answer 3

best solution for your task is:

string zad3 = "ala123alama234ijeszczepsa54dsfd";
string max = Regex.Split(zad3,@"\d+").Max(x => x);

Answer 4

You must change your Regex pattern to include the repetition operator + so that it matches more than once.

[a-zA-Z] should be [a-zA-Z]+

You can get the longest value using LINQ. Order by the match length descending and then take the first entry. If there are no matches the result is null.

string pattern2 = "[a-zA-Z]+";
string zad3 = "ala123alama234ijeszczepsa";

var matches = Regex.Matches(zad3, pattern2);

string result = matches
                 .Cast<Match>()
                 .OrderByDescending(x => x.Value.Length)
                 .FirstOrDefault()?
                 .Value;

The string named result in this example is:

ijeszczepsa