C# how to find and replace specific text in string?

Question

I have a string which represents byte array, inside of it I have several groups of numbers (usually 5): which are encoded as 0x30..0x39 (codes for 0..9 digits). Before and after each number I have a space (0x20 code).

Examples:

"E5-20-32-36-20-E0"                // "32-36" encodes number "26", notice spaces: "20"
"E5-20-37-20-E9"                   // "37" encodes number "7"
"E5-20-38-20-E7-E4-20-37-35-20-E9" // two numbers: "8" (from "38") and "75" (from "37-35")

I want to find out all these groups and reverse digits in the encoded numbers:

   8 -> 8
  75 -> 57
 123 -> 321

Desired outcome:

"E5-20-32-36-20-E0"                   -> "E5-20-36-32-20-E0"
"E5-20-37-20-E9"                      -> "E5-20-37-20-E9"
"E5-20-37-38-39-20-E9"                -> "E5-20-39-38-37-20-E9" 
"E5-20-38-39-20-E7-E4-20-37-35-20-E9" -> "E5-20-39-38-20-E7-E4-20-35-37-20-E9"

I have the data inside a List \ String \ Byte[] - so maybe there is a way to do it ?

Thanks,

but I don;t know what I'm looking for..... I don't now if the number will be 26 or 37.... — David12123
– David12123, Commented Sep 25, 2018 at 9:14
I wrote...... I need to find the numbers inside the message and replace the order — David12123
– David12123, Commented Sep 25, 2018 at 9:17
HOW do you want to replace the order? just reverse them or otherwise? — julian bechtold
– julian bechtold, Commented Sep 25, 2018 at 9:28
@julianbechtold according to the other comments, they want to reverse the order but only if it's a number.. I think? — user9401448
– user9401448, Commented Sep 25, 2018 at 9:29

Dmitrii Bychenko · Accepted Answer · 2018-09-25 11:14:38Z

2

It's unclear (from the original question) what do you want to do with the the digits; let's extract a custom method for you to implement it. As an example, I've implemented reverse:

32          -> 32
32-36       -> 36-32
36-32-37    -> 37-32-36
36-37-38-39 -> 39-38-37-36

Code:

// items: array of digits codes, e.g. {"36", "32", "37"}
//TODO: put desired transformation here
private static IEnumerable<string> Transform(string[] items) {
  // Either terse Linq:
  // return items.Reverse();

  // Or good old for loop:
  string[] result = new string[items.Length];

  for (int i = 0; i < items.Length; ++i)
    result[i] = items[items.Length - i - 1];

  return result;
}

Now we can use regular expressions (Regex) to extract all the digit sequencies and replace them with transformed ones:

  using System.Text.RegularExpressions;

  ...

  string input = "E5-20-36-32-37-20-E0";

  string result = Regex
    .Replace(input, 
           @"(?<=20\-)3[0-9](\-3[0-9])*(?=\-20)", 
             match => string.Join("-", Transform(match.Value.Split('-'))));

  Console.Write($"Before: {input}{Environment.NewLine}After:  {result}";);

Outcome:

Before: E5-20-36-32-37-20-E0
After:  E5-20-37-32-36-20-E0

Edit: In case reverse is the only desired transformation, the code can be simplified by dropping Transform and adding Linq:

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

...

string input = "E5-20-36-32-37-20-E0";

string result = Regex
  .Replace(input, 
          @"(?<=20\-)3[0-9](\-3[0-9])*(?=\-20)", 
           match => string.Join("-", match.Value.Split('-').Reverse()));

More tests:

private static string MySolution(string input) {
  return Regex
    .Replace(input,
           @"(?<=20\-)3[0-9](\-3[0-9])*(?=\-20)",
             match => string.Join("-", Transform(match.Value.Split('-'))));
} 

...

string[] tests = new string[] {
  "E5-20-32-36-20-E0",
  "E5-20-37-20-E9",
  "E5-20-37-38-39-20-E9",
  "E5-20-38-39-20-E7-E4-20-37-35-20-E9",
};

string report = string.Join(Environment.NewLine, tests
  .Select(test => $"{test,-37} -> {MySolution(test)}"));

Console.Write(report);

Outcome:

E5-20-32-36-20-E0                     -> E5-20-36-32-20-E0
E5-20-37-20-E9                        -> E5-20-37-20-E9
E5-20-37-38-39-20-E9                  -> E5-20-39-38-37-20-E9
E5-20-38-39-20-E7-E4-20-37-35-20-E9   -> E5-20-39-38-20-E7-E4-20-35-37-20-E9

Edit 2: Regex explanation (see https://www.regular-expressions.info/lookaround.html for details):

   (?<=20\-)         - must appear before the match: "20-" ("-" escaped with "\")
   3[0-9](\-3[0-9])* - match itself (what we are replacing in Regex.Replace) 
   (?=\-20)          - must appear after the match "-20" ("-" escaped with "\")

Let's have a look at match part 3[0-9](\-3[0-9])*:

   3           - just "3"
   [0-9]       - character (digit) within 0-9 range
   (\-3[0-9])* - followed by zero or more - "*" - groups of "-3[0-9]"

edited Sep 25, 2018 at 11:14

answered Sep 25, 2018 at 9:53

Dmitrii Bychenko

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9 Comments

Mikitori Over a year ago

Pretty good, but it seems he wants full inversion on number indexes. anyway I was working on the regex you just put ^^. @David12123: when in need to test a regex, I love the share this (it may help you): regex101.com

David12123 Over a year ago

I'm sorry - but i can;t seem to understand what i don't explain good - I want to find the numbers in my string array (which is in Hex) and reverse it's order : 12-21,123-321,1234-4321,55-55,1719-9171

Dmitrii Bychenko Over a year ago

@Mikitori: Now (with two digits swapped in the question's only example) we can only guess what the actual transformation should be. That is the very reason I've extracted Transform method

Dmitrii Bychenko Over a year ago

@David12123: OK, I see; let's edit Transform method

Dmitrii Bychenko Over a year ago

@David12123: you are welcome! Next time, please, spend few minutes more to put a question :)

|

Mikitori · Accepted Answer · 2018-09-25 10:01:47Z

1

I'm not sure but I guess the length can change and you just want to reorder in reverse order just the numbers. so a possible way is:

Put the string in 2 arrays (so they are the same)
Iterate through one of them to locate begin and end o fthe number area
Go from end-area to begin-area in first array and write to the second from begin-area to end-area

Edit: not really tested, i just wrote that quickly:

    string input = "E5-20-36-32-37-20-E0";
    string[] array1 = input.Split('-');
    string[] array2 = input.Split('-');

    int startIndex = -1;
    int endIndex = -1;

    for (int i= 0; i < array1.Length; ++i)
    {
        if (array1[i] == "20")
        {
            if (startIndex < 0)
            {
                startIndex = i + 1;
            }
            else
            {
                endIndex = i - 1;
            }
        }
    }

    int pos1 = startIndex;
    int pos2 = endIndex;
    for (int j=0; j < (endIndex- startIndex + 1); ++j)
    {
        array1[pos1] = array2[pos2];
        pos1++;
        pos2--;
    }

edited Sep 25, 2018 at 10:01

answered Sep 25, 2018 at 9:22

Mikitori

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7 Comments

David12123 Over a year ago

this is what I want , and thought to do - but how to do it?

Mikitori Over a year ago

@David12123 just a minute i will type something, but the description is pretty self-explanatory, you should try ^^

David12123 Over a year ago

all this time I have tried - this is why I have ask here :-)

Mikitori Over a year ago

i edited the answer, probably not the most elegant way to do it, but now improving the code is your job, you have the idea ^^

Mikitori Over a year ago

My answer consider only one number area but its size doesn' matter. I put no check at all, be careful when playing with index of an array, going too far is pretty easy, you should add some protections

|

julian bechtold · Accepted Answer · 2018-09-25 10:15:57Z

0

If you would be clear about how you want to process the numbers, it would be easier to provide a solution.

Do you want to swap them randomly?
Do you want to reverse order?
Do you want to swap every second number with the number before?
Do you want to swap ...

you can try the following (for reversing the numbers)

string hex = "E5-20-36-32-20-E0"; // this is your input string

// split the numbers by '-' and generate list out of it
List<string> hexNumbers = new List<string>();
hexNumbers.AddRange(hex.Split('-'));

// find start and end of the numbers that should be swapped
int startIndex = hexNumbers.IndexOf("20");
int endIndex = hexNumbers.LastIndexOf("20");

string newHex = "";
// add the part in front of the numbers that should be reversed
for (int i = 0; i <= startIndex; i++) newHex += hexNumbers[i] + "-";
// reverse the numbers
for (int i = endIndex-1; i > startIndex; i--) newHex += hexNumbers[i] + "-";
// add the part behind the numbers that should be reversed
for (int i = endIndex; i < hexNumbers.Count-1; i++) newHex += hexNumbers[i] + "-";
newHex += hexNumbers.Last();

If the start and the end is always the same, this can be fairly simplified into 4 lines of code:

string[] hexNumbers = hex.Split('-');
string newHex = "E5-20-";
for (int i = hexNumbers.Count() - 3; i > 1; i--) newHex += hexNumbers[i] + "-";
newHex += "20-E0";

Results:

"E5-20-36-32-20-E0" -> "E5-20-32-36-20-E0"
"E5-20-36-32-37-20-E0"    -> "E5-20-32-37-36-20-E0"
"E5-20-36-12-18-32-20-E0" -> "E5-20-32-18-12-36-20-E0"

edited Sep 25, 2018 at 10:15

answered Sep 25, 2018 at 9:24

julian bechtold

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3 Comments

David12123 Over a year ago

first time use of Regex , so please explain (if you can) - also I get this error: Severity Code Description Project File Line Suppression State Error CS0019 Operator '&&' cannot be applied to operands of type 'Match' and 'bool' ReadSerailData

David12123 Over a year ago

I want to swap the order,not random - so when I find 0x39,0x34 -- I want to change it to :0x34,0x39. and if I have 0x36,0x37,0x31 - it will be 0x31,0x37,0x36

julian bechtold Over a year ago

sorry @david my code was totally untested - this code should now work as of your request. Regex (regular expressions) are a speciall format to match strings. for example [0-9] matches any number between 0-9. [0-9]+ matcvhes any number from 0 - infinite. definitely worth a look

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