C# Reverse all numbers in string?

Question

I have a string:

"Hello 7866592 this is my 12432 string and 823 i need to flip all 123"

And i want to to be

"Hello 2956687 this is my 23421 string and 328 i need to flip all 321"

I use this regular expression to get all numbers:

Regex nums = new Regex("\d+");

There are no normal regular expression language elements that will do this for you. You don't say whether you need the solution to be a regular expression (and that would be a very long and difficult regex, if you can even do it). That means you seem to be looking for a normal programming solution for a basic problem. I don't think this is appropriate for stackoverflow. — Alan McBee
– Alan McBee, Commented Jun 21, 2012 at 18:49
Sounds like homework. Using regular expressions would be good to extract the numbers, but I reckon it'd be best to just increment through the string as an array of chars, record an index point where a set of digits start, then increment until you reach a non-digit, then look at reversing the digits in between index points a and b-1. — Adrian Thompson Phillips
– Adrian Thompson Phillips, Commented Jun 21, 2012 at 18:51

Yuriy Faktorovich · Accepted Answer · 2012-06-21 18:57:41Z

21

var replacedString = 
    Regex.Replace(//finds all matches and replaces them
    myString, //string we're working with
    @"\d+", //the regular expression to match to do a replace
    m => new string(m.Value.Reverse().ToArray())); //a Lambda expression which
        //is cast to the MatchEvaluator delegate, so once the match is found, it  
        //is replaced with the output of this method.

edited Jun 21, 2012 at 18:57

answered Jun 21, 2012 at 18:49

Yuriy Faktorovich

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5 Comments

user166390 Over a year ago

The important bit here is the replacer function. (Just be glad this isn't Java!)

Danpe Over a year ago

Error: Cannot convert lambda expression to type 'string'

Yuriy Faktorovich Over a year ago

@Danpe sorry fixed, meant to do the Regex.Replace, but was typing in a browser.

Danpe Over a year ago

Man, you are just awesome! I whould like if you can add explenation of how it works exactly :)

Steve Wortham Over a year ago

+1. Couldn't haven written it better myself. This overload of Regex.Replace utilizes the MatchEvaluator, which allows you to perform any operation you'd like on each individual match.

Justin · Accepted Answer · 2012-06-21 18:49:12Z

1

Split the string on spaces. Then take the strings in the new string array that are digits and run this function on them:

public static string Reverse( string s )
{
   char[] charArray = s.ToCharArray();
   Array.Reverse( charArray );
   return new string( charArray );
}

Then recombine your array into a single string.

answered Jun 21, 2012 at 18:49

Justin

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