Regex replace multiple groups

Similar to Jamiec's answer, but this allows you to use regexes that don't match the text exactly, e.g. \. can't be used with Jamiec's answer, because you can't look up the match in the dictionary.

This solution relies on creating groups, looking up which group was matched, and then looking up the replacement value. It's a more complicated, but more flexible.

First make the map a list of KeyValuePairs

var map = new List<KeyValuePair<string, string>>();           
map.Add(new KeyValuePair<string, string>("\.", "dot"));

Then create your regex like so:

string pattern = String.Join("|", map.Select(k => "(" + k.Key + ")"));
var regex = new Regex(pattern, RegexOptions.Compiled);

Then the match evaluator becomes a bit more complicated:

private static string Evaluator(List<KeyValuePair<string, string>> map, Match match)
{            
    for (int i = 0; i < match.Groups.Count; i++)
    {
        var group = match.Groups[i];
        if (group.Success)
        {
            return map[i].Value;
        }
    }

    //shouldn't happen
    throw new ArgumentException("Match found that doesn't have any successful groups");
}

Then call the regex replace like so:

var newString = regex.Replace(text, m => Evaluator(map, m))

Given a dictionary that defines your replacements:

IDictionary<string, string> map = new Dictionary<string, string>()
{
    {"&","__amp"},
    {"#","__hsh"},
    {"1","5"},
    {"5","6"},
};

You can use this both for constructing a Regular Expression, and to form a replacement for each match:

var str = "a1asda&fj#ahdk5adfls";
var regex = new Regex(String.Join("|",map.Keys));
var newStr = regex.Replace(str, m => map[m.Value]);
// newStr = a5asda__ampfj__hshahdk6adfls

Live example: http://rextester.com/rundotnet?code=ADDN57626

This uses a Regex.Replace overload which allows you to specify a lambda expression for the replacement.

---

It has been pointed out in the comments that a find pattern which has regex syntax in it will not work as expected. This could be overcome by using Regex.Escape and a minor change to the code above:

var str = "a1asda&fj#ahdk5adfls";
var regex = new Regex(String.Join("|",map.Keys.Select(k => Regex.Escape(k))));
var newStr = regex.Replace(str, m => map[m.Value]);
// newStr = a5asda__ampfj__hshahdk6adfls

Given a dictionary like in the other answers, you can use an "aggregate" to map each pattern in the dictionary to a replacement. This will give you far more flexibility that the other answers, as you can have different regex options for each pattern.

For example, the following code will "romanize" greek text (https://en.wikipedia.org/w/index.php?title=Romanization_of_Greek&section=3#Modern_Greek, Standard/UN):

var map = new Dictionary<string,string>() {
    {"α[ύυ](?=[άαβγδέεζήηίΐϊιλμνόορύΰϋυώω])", "av"}, {"α[ύυ]", "af"}, {"α[ϊΐ]", "aï"}, {"α[ιί]", "ai"}, {"[άα]", "a"},
    {"β", "v"}, {"γ(?=[γξχ])", "n"}, {"γ", "g"}, {"δ", "d"},
    {"ε[υύ](?=[άαβγδέεζήηίΐϊιλμνόορύΰϋυώω])", "ev"}, {"ε[υύ]", "ef"}, {"ει", "ei"}, {"[εέ]", "e"}, {"ζ", "z"},
    {"η[υύ](?=[άαβγδέεζήηίΐϊιλμνόορύΰϋυώω])", "iv"}, {"η[υύ]", "if"}, {"[ηήιί]", "i"}, {"[ϊΐ]", "ï"},
    {"θ", "th"}, {"κ", "k"}, {"λ", "l"}, {"\\bμπ|μπ\\b", "b"}, {"μπ", "mb"}, {"μ", "m"}, {"ν", "n"},
    {"ο[ιί]", "oi"}, {"ο[υύ]", "ou"}, {"[οόωώ]", "o"}, {"ξ", "x"}, {"π", "p"}, {"ρ", "r"},
    {"[σς]", "s"}, {"τ", "t"}, {"[υύϋΰ]", "y"}, {"φ", "f"}, {"χ", "ch"}, {"ψ", "ps"}
};

var input = "Ο Καλύμνιος σφουγγαράς ψυθίρισε πως θα βουτήξει χωρίς να διστάζει."; 
map.Aggregate(input, (i, m) => Regex.Replace(i, m.Key, m.Value, RegexOptions.IgnoreCase));

returning (without modifying the "input" variable:

"o kalymnios sfoungaras psythirise pos tha voutixei choris na distazei."

You can of course use something like:

foreach (var m in map) input = Regex.Replace(input, m.Key, m.Value, RegexOptions.IgnoreCase);

which does modify the "input" variable.

Also you can add this to improve performance:

var remap = new Dictionary<Regex, string>();
foreach (var m in map) remap.Add(new Regex(m.Key, RegexOptions.IgnoreCase | RegexOptions.Compiled), m.Value);

cache or make static the remap dictionary and then use:

remap.Aggregate(input, (i, m) => m.Key.Replace(i, m.Value));

How about using string.Replace()?

string foo = "a1asda&fj#ahdk5adfls"; 

string bar = foo.Replace("&","__amp")
                .Replace("#","__hsh")
                .Replace("5", "6")
                .Replace("1", "5");