CODEWITHSUNDEEP
c#stringreplace
Byte Commander
Byte Commander

Reputation: 6736

How to remove all but the first occurences of a character from a string?

I have a string of text and want to ensure that it contains at most one single occurrence of a specific character (,). Therefore I want to keep the first one, but simply remove all further occurrences of that character.

How could I do this the most elegant way using C#?

Upvotes: 2

Views: 3285

Answers (7)

Rion Williams
Rion Williams

Reputation: 76547

You could write a function like the following one that would split the string into two sections based on the location of what you were searching (via the String.Split() method) for and it would only remove matches from the second section (using String.Replace()) :

public static string RemoveAllButFirst(string s, string stuffToRemove)
{
    // Check if the stuff to replace exists and if not, return the original string
    var locationOfStuff = s.IndexOf(stuffToRemove);
    if (locationOfStuff < 0)
    {
        return s;
    }
    // Calculate where to pull the first string from and then replace the rest of the string
    var splitLocation = locationOfStuff + stuffToRemove.Length;
    return s.Substring(0, splitLocation) +  (s.Substring(splitLocation)).Replace(stuffToRemove,"");
}

You could simply call it by using :

var output = RemoveAllButFirst(input,",");

A prettier approach might actually involve building an extension method that handled this a bit more cleanly :

public static class StringExtensions
{
     public static string RemoveAllButFirst(this string s, string stuffToRemove)
     {
           // Check if the stuff to replace exists and if not, return the 
           // original string
           var locationOfStuff = s.IndexOf(stuffToRemove);
           if (locationOfStuff < 0)
           {
               return s;
           }
           // Calculate where to pull the first string from and then replace the rest of the string
           var splitLocation = locationOfStuff + stuffToRemove.Length;
           return s.Substring(0, splitLocation) +  (s.Substring(splitLocation)).Replace(stuffToRemove,"");
     }
}

which would be called via :

var output = input.RemoveAllButFirst(",");

You can see a working example of it here.

Upvotes: 2

Mattias &#197;slund
Mattias &#197;slund

Reputation: 3907

Pretty short with Linq; split string into chars, keep distinct set and join back to a string.

text = string.Join("", text.Select(c => c).Distinct());

Upvotes: -1

Nursultan Aidarkulov
Nursultan Aidarkulov

Reputation: 128

    static string KeepFirstOccurance(this string str, char c)
    {
        int charposition = str.IndexOf(c);
        return str.Substring(0, charposition + 1) +
                   str.Substring(charposition, str.Length - charposition)
                   .Replace(c, ' ').Trim();
    }

Upvotes: 0

Nikola.Lukovic
Nikola.Lukovic

Reputation: 1325

If you don't deal with large strings and you reaaaaaaly like Linq oneliners:

public static string KeepFirstOccurence (this string @string, char @char)
{
    var index = @string.IndexOf(@char);
    return String.Concat(String.Concat(@string.TakeWhile(x => @string.IndexOf(x) < index + 1)), String.Concat(@string.SkipWhile(x=>@string.IndexOf(x) < index)).Replace(@char.ToString(), ""));
}

Upvotes: 1

Tim Schmelter
Tim Schmelter

Reputation: 460068

You could use a counter variable and a StringBuilder to create the new string efficiently:

var sb = new StringBuilder(text.Length);
int maxCount = 1;
int currentCount = 0;
char specialChar = ',';
foreach(char c in text)
    if(c != specialChar || ++currentCount <= maxCount)
        sb.Append(c);
text = sb.ToString();

This approach is not the shortest but it's efficient and you can specify the char-count to keep.

Here's a more "elegant" way using LINQ:

int commasFound = 0; int maxCommas = 1;
text = new string(text.Where(c => c != ',' || ++commasFound <= maxCommas).ToArray());

I don't like it because it requires to modify a variable from a query, so it's causing a side-effect.

Upvotes: 2

Rawling
Rawling

Reputation: 50104

Regular expressions are elegant, right?

Regex.Replace("Eats, shoots, and leaves.", @"(?<=,.*),", "");

This replaces every comma, as long as there is a comma before it, with nothing.

(Actually, it's probably not elegant - it may only be one line of code, but it may also be O(n^2)...)

Upvotes: 1

jackomelly
jackomelly

Reputation: 543

This works, but not the most elegant for sure :-) 

string a = "12,34,56,789";
int pos = 1 + a.IndexOf(',');
return a.Substring(0, pos) + a.Substring(pos).Replace(",", string.Empty);

Upvotes: 4

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