LINQ conditional selection and formatting

Question

I have a string of characters and I'm trying to set up a query that'll substitute a specific sequence of similar characters into a character count. Here's an example of what I'm trying to do:

agd69dnbd 555 bdggjykbcx 555555 bbb

In this case, I'm trying to isolate and count ONLY the occurrences of the number 5, so my output should read:

agd69dnbd 3 bdggjykbcx 6 bbb

My current code is the following, where GroupAdjacentBy is a function that groups and counts the character occurrences as above.

var res = text
.GroupAdjacentBy((l, r) => l == r)
.Select(x => new { n = x.First(), c = x.Count()})
.ToArray();

The problem is that the above function groups and counts EVERY SINGLE character in my string, not the just the one character I'm after. Is there a way to conditionally perform that operation on ONLY the character I need counted?

Answer 1

Regex is a better tool for this job than LINQ.

Have a look at this:

string input = "agd69dnbd555bdggjykbcx555555bbb";

string pattern = @"5+"; // Match 1 or more adjacent 5 character

string output = Regex.Replace(input, pattern, match => match.Length.ToString());

// output = agd69dnbd3bdggjykbcx6bbb

Not sure if your intending to replace every 5 character, or just when there is more than one adjacent 5.

If it's the latter, just change your pattern to:

string pattern = @"5{2,}"; // Match 2 or more adjacent 5's

Answer 2

The best answer was already given by Johnathan Barclay. But just for the case that you need something similar by using Linq and to show an alternative solution:

var charToCombine = '5';
var res = text
    .GroupAdjacentBy((l, r) => l == r )
    .SelectMany(x => x.Count() > 1 && x.First() == charToCombine ? x.Count().ToString() : x)
    .ToArray();