Extract index numbers from list of string

Question

I have a list of strings where those strings have an index in each string and I need to extract the index from that string and put it in a List<int> .

Here's is a list example:

List<string> values = new List<string>();
values.Add("cohabitantGender");
values.Add("additionalDriver0LastName");
values.Add("additionalDriver0AgeWhenLicensed");
values.Add("vehicle0City");
values.Add("vehicle1City");
values.Add("vehicle2City");
values.Add("vehicle3City");

from this list I need to extract the indexes from the values vehicleXCity . I have this code right now:

public static List<int> FormObjectIndexExtractor(List<string> values, string prefix, string suffix)
{
    var selectedMatches = values.Where(v => v.StartsWith(prefix) && v.EndsWith(suffix)).Select(v=> v).ToList();
    var indexes = new List<int>();
    foreach (var v in selectedMatches) indexes.Add(int.Parse(Regex.Match(v, @"\d+").Value));
    return indexes;
}

And I'm using it like this:

List<int> indexes = FormObjectIndexExtractor(values, "vehicle", "City");

But if I have a value like vehicle4AnotherCity the code will work in the wrong way.

Does anyone have some alternative to this code that may help?

Answer 1

Below is an extension helper class incase you have a more robust list and you require multiple exclusion options

public class INumberList : List<string>
{ 
    public List<int> GetNumberList()
    {
        List<int> numberList = new List<int>();
        for (int i = 0; i < this.Count; i++)
        {
            numberList.Add(GetIntFromString(this[i]));
        }
        return numberList;
    } 
    public INumberList ExcludeIndex(string prefix, string suffix)
    {
        for (int i = 0; i < this.Count; i++)
        { 
            if (this[i].StartsWith(prefix) && this[i].EndsWith(suffix))
            {
                //remove non needed indexes
                this.RemoveAt(i);
            }
        }
        return this;
    }
    public static int GetIntFromString(String input)
    {
        // Replace everything that is no a digit.
        String inputCleaned = Regex.Replace(input, "[^0-9]", "");

        int value = 0;

        // Tries to parse the int, returns false on failure.
        if (int.TryParse(inputCleaned, out value))
        {
            // The result from parsing can be safely returned.
            return value;
        }

        return 0; // Or any other default value.
    }
}

Then use like this:

INumberList values = new INumberList();
        values.Add("cohabitantGender");
        values.Add("additionalDriver0LastName");
        values.Add("additionalDriver0AgeWhenLicensed");
        values.Add("vehicle0City");
        values.Add("vehicle1City");
        values.Add("vehicle2City");
        values.Add("vehicle3City");
//Get filtered index list with multiple exclusion option
List<int> indexList = values.ExcludeIndex("cohabitantGender","")
                        .ExcludeIndex("additionalDriver","AgeWhenLicensed")
                        .GetNumberList(); 
//will return [0,0,1,2,3]

Answer 2

Here is a solution (using modern C# features) that does not use Regex :

public static List<int> FormObjectIndexExtractor(IEnumerable<string> values, string prefix, string suffix)
{
  int? TryParseItem(string val)
  {
    if (val.Length <= prefix.Length + suffix.Length || !val.StartsWith(prefix) || !val.EndsWith(suffix))
      return null;

    var subStr = val.Substring(prefix.Length, val.Length - prefix.Length - suffix.Length);

    if (int.TryParse(subStr, out var number))
      return number;

    return null;
  }

  return values.Select(TryParseItem).Where(v => v.HasValue).Select(v => v.Value).ToList();
}

Answer 3

Try this:

public static List<int> FormObjectIndexExtractor(List<string> values, string prefix, string suffix)
{
    var s = "^" + prefix + @"(\d+)\.*?" + suffix + "$";
    return values
            .Where(v => Regex.Match(v, s).Success)
            .Select(v=> int.Parse(Regex.Match(v, s).Groups[1].Value))
            .ToList();
}

Answer 4

This version splits all the parts of string.

public static List<int> FormObjectIndexExtractor(List<string> values, string prefix, string suffix)
{
    List<int> ret = new List<int>();
    Regex r = new Regex("^([a-zA-Z]+)(\\d+)([a-zA-Z]+)$");
    foreach (var s in values)
    {
        var match = r.Match(s);
        if (match.Success)
        {
            if (match.Groups[1].ToString() == prefix && match.Groups[3].ToString() == suffix)
            {
                ret.Add(int.Parse(match.Groups[2].ToString()));
            }
        }
    }
    return ret;
}

or alternatively:

public static List<int> FormObjectIndexExtractor(List<string> values, string prefix, string suffix)
{
    List<int> ret = new List<int>();
    Regex r = new Regex($"^{prefix}(\d+){suffix}$");
    foreach (var s in values)
    {
        var match = r.Match(s);
        if (match.Success)
        {
            ret.Add(int.Parse(match.Groups[1].ToString()));
        }
    }
    return ret;
}

Answer 5

This is the more generic version.

1. Regex match:

   • starts with 'vehicle'
   • matches a number
   • ends with 'city'.

2. Parse and return as List<int>

     var indexes = values.Where(a => Regex.IsMatch(a, @"^vehicle\\d+City$")). Select(k => int.Parse(Regex.Match(k, @"\\d+").Value)).ToList();