The given key was not present in the dictionary Match Evaluator delegate

Question

I'm trying to replace a string with regex via Match Evaluator delegate. [dictionary method] when the string starts with: .- &*?. I get a error with the following details:

the given key was not present in the dictionary.

What can I do?

IDictionary<string, string> dict = new Dictionary<string, string> ()
{
    { "-", "e"  },
    { "?", "z'" },
};

string str1 = "-50"
var p = new Regex(String.Join("|", dict.Keys));
str2 = p.Replace(str1, x => dict[x.Value]);

Dmitry Bychenko · Accepted Answer · 2023-02-09T23:49:55.847

You should Escape symbols (e.g. ?) which have special meaning in regular expressions:

using System.Linq;
using System.Text.RegularExpressions;

...

IDictionary<string, string> dict = new Dictionary<string, string>() {
  { "-", "e"  },
  { "?", "z'" }, 
};

var pattern = string.Join("|", dict
  .Keys
  .OrderByDescending(key => key.Length)
  .Select(key => Regex.Escape(key)));

string str1 = "-50";

string str2 = Regex.Replace(str1, pattern, match => dict[match.Value]);

There is a little trick with .OrderByDescending(key => key.Length): if we have pattern which is a substring of another one, say

{"--", "x2"},
{"-", "x1"},  // "-" is a substring of "--"

then we should try longer pattern first: --abc should be transformed into x2abc, not x1x1abc

The given key was not present in the dictionary Match Evaluator delegate

1 Answers1