Replace multiple words in a string from a list of words

Question

i have a list of words:

string[] BAD_WORDS = { "xxx", "o2o" } // My list is actually a lot bigger about 100 words

and i have some text (usually short , max 250 words), which i need to REMOVE all the BAD_WORDS in it.

i have tried this:

    foreach (var word in BAD_WORDS)
    {
        string w = string.Format(" {0} ", word);
        if (input.Contains(w))
        {
            while (input.Contains(w))
            {
                input = input.Replace(w, " ");
            }
        }
    }

but, if the text starts or ends with a bad word, it will not be removed. i did it with the spaces, so it will not match partial words for example "oxxx" should not be removed, since it is not an exact match to the BAD WORDS.

anyone can give me advise on this?

Why have you included this line string w = string.Format(" {0} ", word);? — Nikhil Agrawal
– Nikhil Agrawal, Commented Sep 1, 2012 at 9:54
what is your questing, your code looks fine? Just remove the if and do a startswith and ends with. — Peter
– Peter, Commented Sep 1, 2012 at 9:54
@Nikhil Agrawal: To put spaces before and after. If you keep just the word it will also match oxxx for example. — Tudor
– Tudor, Commented Sep 1, 2012 at 9:54
Your if is unnecessary. It's better to start out with the while to avoid checking twice the first time. — Tim S.
– Tim S., Commented Sep 1, 2012 at 12:39

Yuriy Zaletskyy · Accepted Answer · 2017-12-27 15:19:45Z

18

string cleaned = Regex.Replace(input, "\\b" + string.Join("\\b|\\b",BAD_WORDS) + "\\b", "")

edited Dec 27, 2017 at 15:19

Yuriy Zaletskyy

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answered Sep 1, 2012 at 9:55

shannon

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4 Comments

shannon Over a year ago

Hold a moment, I missed something... working... There, fixed. :)

shannon Over a year ago

Hee... :) Thanks Dementic. Do as I say, not as I do. I was only trying to say that all the nesting and LINQing and looping had a simple older/tried-and-true method.

Jon Hanna Over a year ago

+1 for catching words at start or other boundary conditions. As a bonus, if the replace needs to be done multiple times, the regex produced can be cached for repeated use. I'd use Regex.Escape though just in case BAD_WORDS contained something significant to the regex syntax.

Tim S. Over a year ago

Maybe not perfect code as others have pointed out improvements, but +1 for using regex word boundaries instead of splitting.

James Ellis-Jones · Accepted Answer · 2019-11-13 15:44:51Z

6

This is a great task for Linq, and also the Split method. Try this:

return string.Join(" ", input.Split(' ').Where(w => !BAD_WORDS.Contains(w)));

edited Nov 13, 2019 at 15:44

answered Sep 1, 2012 at 9:55

James Ellis-Jones

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3 Comments

Jon Hanna Over a year ago

As long as spaces suffice. This won't catch the words at the start or end, if followed by a newline, if followed by punctuation etc. If that case needs to be dealt with, the regex-based answers will do a better job.

Professor Zoom Over a year ago

This is adding extra spaces between words and I don't know why

James Ellis-Jones Over a year ago

The empty string was being joined with a space on both sides to the other items. I've edited the answer (and it's now neater!)

Kundan Singh Chouhan · Accepted Answer · 2012-09-01 09:51:56Z

1

You could use StartWith and EndsWith methods like:

while (input.Contains(w) || input.StartsWith(w) || input.EndsWith(w) || input.IndexOf(w) > 0)
{
   input = input.Replace(w, " ");
}

Hope this will fix your problem.

answered Sep 1, 2012 at 9:51

Kundan Singh Chouhan

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2 Comments

Tudor Over a year ago

Don't you mean OR not AND? With your test it must simultaneously start, end and contain the word.

Rafael Herscovici Over a year ago

this will still catch partial words (badword = 'aoooo', actual word='aoooome', it will remove the 'aoooo'.

Jeremy Thompson · Accepted Answer · 2012-09-01 09:52:04Z

1

Put the fake space's before and after the string varaible input. That way it will detect the first and last words.

input = " " + input + " ";

 foreach (var word in BAD_WORDS)
    {
        string w = string.Format(" {0} ", word);
        if (input.Contains(w))
        {
            while (input.Contains(w))
            {
                input = input.Replace(w, " ");
            }
        }
    }

Then trim the string:

input = input.Trim();

answered Sep 1, 2012 at 9:52

Jeremy Thompson

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1 Comment

Rafael Herscovici Over a year ago

that is a good idea, that will fix my code, but isnt there a nicer solution to this? the code seems a little weird do me, i wrote it because i had no other idea.

Antonio Bakula · Accepted Answer · 2012-09-01 10:01:58Z

1

You can store words from text to one list. Then just check all words if they are in bad list, something like this :

List<string> myWords = input.Split(' ').ToList();
List<string> badWords = GetBadWords();

myWords.RemoveAll(word => badWords.Contains(word));
string Result = string.Join(" ", myWords);

edited Sep 1, 2012 at 10:01

answered Sep 1, 2012 at 9:55

Antonio Bakula

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Comments

David Limkys · Accepted Answer · 2012-09-01 10:10:38Z

0

Just wanted to point out that you shoulde have done with just whiole inside your for like so:

   foreach (var word in BAD_WORDS)
{
    while (input.Contains(String.Format(" {0} ", word);))
    {
        input = input.Replace(w, " ");
    }
}

No need for that if and 'w' variable, in any case i wouldehave used the answer above me that Antonio Bakula, first think that came to mind was this.

answered Sep 1, 2012 at 10:10

David Limkys

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1 Comment

Rafael Herscovici Over a year ago

You are trying to replace w which you have removed from the code. without the w, it will replace partial word matches also.

Community · Accepted Answer · 2017-05-23 11:59:57Z

0

According to the following post the fastest way is to use Regex and MatchEvaluator : Replacing multiple characters in a string, the fastest way?

        Regex reg = new Regex(@"(o2o|xxx)");
        MatchEvaluator eval = match =>
        {
            switch (match.Value)
            {
                case "o2o": return " ";
                case "xxx": return " ";
                default: throw new Exception("Unexpected match!");
            }
        };
        input = reg.Replace(input, eval);

edited May 23, 2017 at 11:59

CommunityBot

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answered Jul 20, 2015 at 8:25

Yanga

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