Extract values from a string based on a pattern

Question

I need to pull a bunch of key value pairs based on a predefined pattern from a string. An example of what I would need is this:

Pattern: {value1}-{value2}

String: Example-String

Result KVP:

{ Key: value1, value: Example }, { Key: value2, value: String }

The catch is that the pattern could be pretty much anything (although the values I'd need to extract would always be surrounded in curly brackets), ie:

Pattern: {test1}\{test2}={value}

String: Example\Value=Result

Result KVP:

{ Key: test1, value: Example }, { Key: test2, value: Value }, { Key: value, value: Result }

What I have done so far isn't quite working and I'm quite certain that there has to be a more elegant way of doing this as opposed to my solution anyway so I thought I'd see if anyone here would have a good idea.

EDIT:

Here is essentially what I have so far (it's working, but IMO it's really ugly):

public List<KeyValuePair<string, string>> Example(string pattern, string input) { var values = new List<KeyValuePair<string, string>>(); var r1 = Regex.Matches(input, @"(\{[A-Z,a-z]*\})"); string newregex = string.Empty; foreach (Match item in r1) { newregex = newregex.Replace(item.Value, "(.*?)"); //updates regex so that it adds this as a group for use later, ie: "{item1}-{item2}" will become "(.*?)-{item2}" string field = item.Value.Substring(1, item.Value.Length - 2); // {test1} will return "test1" values.Add(new KeyValuePair<string, string>(field, string.Empty)); } newregex = $"{newregex}\\z"; // ensures that it matches to end of input var r2 = Regex.Match(input, newregex); // KVP index (used below) int val = 0; foreach (Group g in r2.Groups) { if (g.Value == input) continue; // first group will be equal to input, ignore values[val] = new KeyValuePair<string, string>(values[val].Key, g.Value); // update KVP at index with new KVP with the value val++; } return values; }

Do you have a predefined list of delimeters (like '-' and '='), or at least some rule that defines a delimeter (i.e. any non-alphanumeric character)? — littlerufe
– littlerufe, Commented Nov 18, 2019 at 19:37
@RufusL currently we're only using '-' and '_'. I was hoping to come up with a general solution in case in future we have a need for different delimiters though. — BKF
– BKF, Commented Nov 18, 2019 at 19:40
Are you looking for a method that takes in two strings (a pattern and a search string) and returns a List<KeyValuePair>? It would be extremely helpful to see what you have done so far so we can see where it's not working. — littlerufe
– littlerufe, Commented Nov 18, 2019 at 19:41
@RufusL essentially, yes, a method like that would be ideal. I'll edit my post with what I have done shortly. — BKF
– BKF, Commented Nov 18, 2019 at 19:42

littlerufe · Accepted Answer · 2019-11-18 20:55:59Z

Unfortunately I don't know regular expressions very well, but one way to solve this is to walk through each character of the pattern string and create a list of keys and delimeters, after which we can walk through the search string, and find the index of each delimeter to get the current value, and then add a new KeyValuePair to a list.

Here's a rough sample that assumes good input:

public static List<KeyValuePair<string, string>> GetKVPs(string pattern, string search) { var results = new List<KeyValuePair<string, string>>(); var keys = new List<string>(); var delimeters = new List<string>(); var currentKey = string.Empty; var currentDelimeter = string.Empty; var processingKey = false; // Populate our lists of Keys and Delimeters foreach (var chr in pattern) { switch (chr) { case '}': { if (currentKey.Length > 0) { keys.Add(currentKey); currentKey = string.Empty; } processingKey = false; break; } case '{': { if (currentDelimeter.Length > 0) { delimeters.Add(currentDelimeter); currentDelimeter = string.Empty; } processingKey = true; break; } default: { if (processingKey) { currentKey += chr; } else { currentDelimeter += chr; } break; } } } if (currentDelimeter.Length > 0) delimeters.Add(currentDelimeter); var lastDelim = -1; // Find our Values based on the delimeter positions in the search string for (int i = 0; i < delimeters.Count; i++) { var delimIndex = search.IndexOf(delimeters[i], lastDelim + 1); if (delimIndex > -1) { var value = search.Substring(lastDelim + 1, delimIndex - lastDelim - 1); results.Add(new KeyValuePair<string, string>(keys[i], value)); lastDelim = delimIndex + delimeters[i].Length - 1; } } // Add the item after the final delimeter if it exists: if (lastDelim > -1 && lastDelim < search.Length - 1) { results.Add(new KeyValuePair<string, string>(keys.Last(), search.Substring(lastDelim + 1))); } return results; }

And an example of it in action:

public static void Main(string[] args) { var results = GetKVPs( "{greeting}, {recipient}, this is {sender}.", "Hello, Dolly, this is Louis."); foreach (var kvp in results) { Console.WriteLine($"{kvp.Key} = {kvp.Value}"); } GetKeyFromUser("\nDone! Press any key to exit..."); }

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