Find keyword in text when keyword match certain conditions - C#

Question

I\'m looking for a nice way to do the following:

I have an article which has HTML tags in it like anchors and paragraphs and so on.
I also have keyword which i

Answer 1

I have managed to get it done!

Very much thanks to this post which helped me a lot with the xpath expression: http://social.msdn.microsoft.com/Forums/en-US/regexp/thread/beae72d6-844f-4a9b-ad56-82869d685037/

My task was to add X keywords to the article using table of keywords and urls on my database.
Once keyword was matched - it won't search for it again, but will try to find the next keyword in the text.
The 'keyword' could have been made of more than one word. That's why i added the Replace(" ", "\s+").
Also, i had to give precedence to the longest keywords first. That is if i had:
"good day" and "good" as two different keywords - "good day" always wins.

This is my solution:

static public string AddLinksToArticle(string article, int linksToAdd)
    {
        try
        {
            //load keywords and urls
            var dt = new DAL().GetArticleLinks();

            //sort the it
            IEnumerable<ArticlesRow> sortedArticles = dt.OrderBy(row => row.keyword, new StringLengthComparer());

            // iterate the dictionary to get keyword to replace with anchor
            foreach (var item in sortedArticles)
            {
                article = FindAndReplaceKeywordWithAnchor(article, item.keyword, item.url, ref linksToAdd);
                if (linksToAdd == 0)
                {
                    break;
                }
            }

            return article;
        }
        catch (Exception ex)
        {
            Utils.LogErrorAdmin(ex);
            return null;
        }
    }

    private static string FindAndReplaceKeywordWithAnchor(string article, string keyword, string url, ref int linksToAdd)
    {
        //convert text to html
        HtmlAgilityPack.HtmlDocument doc = new HtmlAgilityPack.HtmlDocument();
        doc.LoadHtml(article);

        // \w* - means it can start with any alphanumeric charactar
        // \s+ - was placed to replace all white spaces (when there is more than one word).
        // \b - set bounderies for the keyword
        string pattern = @"\b" + keyword.Trim().Insert(0, "\\w*").Replace(" ", "\\s+") + @"\b";

        //get all elements text propery except for anchor element 
        var nodes = doc.DocumentNode.SelectNodes("//text()[not(ancestor::a)]") ?? new HtmlAgilityPack.HtmlNodeCollection(null);
        foreach (var node in nodes)
        {
            if (node.InnerHtml.Contains(keyword))
            {
                Regex regex = new Regex(pattern);
                node.InnerHtml = regex.Replace(node.InnerHtml, "<a href=\"" + url + "\">" + keyword + "</a>", 1);//match only first occurrence
                linksToAdd--;
                break;
            }
        }

        return doc.DocumentNode.OuterHtml;
    }
}

public class StringLengthComparer : IComparer<string>
{
    public int Compare(string x, string y)
    {
        return y.Length.CompareTo(x.Length);
    }
}

Hope it will help someone in the future.