Search keyword highlight in ASP.Net

Question

I am outputting a list of search results for a given string of keywords, and I want any matching keywords in my search results to be highlighted. Each word should be wrapped in a span or similar. I am looking for an efficient function to do this.

E.g.

Keywords: "lorem ipsum"

Result: "Some text containing lorem and ipsum"

Desired HTML output: "Some text containing <span class="hit">lorem</span> and <span class="hit">ipsum</span>"

My results are case insensitive.

Answer 1

Here's what I've decided on. An extension function that I can call on the relevant strings within my page / section of my page:

public static string HighlightKeywords(this string input, string keywords)
{
    if (input == string.Empty || keywords == string.Empty)
    {
        return input;
    }

    string[] sKeywords = keywords.Split(' ');
    foreach (string sKeyword in sKeywords)
    {
        try
        {
            input = Regex.Replace(input, sKeyword, string.Format("<span class=\"hit\">{0}</span>", "$0"), RegexOptions.IgnoreCase);
        }
        catch
        {
            //
        }
    }
    return input;
}

Any further suggestions or comments?

Answer 2

try highlighter from Lucene.net

http://incubator.apache.org/lucene.net/docs/2.0/Highlighter.Net/Lucene.Net.Highlight.html

How to use:

http://davidpodhola.blogspot.com/2008/02/how-to-highlight-phrase-on-results-from.html

EDIT: As long as Lucene.net highlighter is not suitable here new link:

http://mhinze.com/archive/search-term-highlighter-httpmodule/

Answer 3

Use the jquery highlight plugin.

For highlighting it at server side

protected override void Render( HtmlTextWriter writer )
{
    StringBuilder html = new StringBuilder();
    HtmlTextWriter w = new HtmlTextWriter( new StringWriter( html ) );

    base.Render( w );

    html.Replace( "lorem", "<span class=\"hit\">lorem</span>" );

    writer.Write( html.ToString() );
}

You can use regular expressions for advanced text replacing.

You can also write the above code in an HttpModule so that it can be re used in other applications.

Answer 4

An extension to the answer above. (don't have enough reputation to give comment)

To avoid span from being replaced when search criteria were [span pan an a], the found word was replaced to something else than replace back... not very efficient though...

public string Highlight(string input)
{
    if (input == string.Empty || searchQuery == string.Empty)
    {
        return input;
    }

    string[] sKeywords = searchQuery.Replace("~",String.Empty).Replace("  "," ").Trim().Split(' ');
    int totalCount = sKeywords.Length + 1;
    string[] sHighlights = new string[totalCount];
    int count = 0;

    input = Regex.Replace(input, Regex.Escape(searchQuery.Trim()), string.Format("~{0}~", count), RegexOptions.IgnoreCase);
    sHighlights[count] = string.Format("<span class=\"highlight\">{0}</span>", searchQuery);
    foreach (string sKeyword in sKeywords.OrderByDescending(s => s.Length))
    {
        count++;
        input = Regex.Replace(input, Regex.Escape(sKeyword), string.Format("~{0}~", count), RegexOptions.IgnoreCase);
        sHighlights[count] = string.Format("<span class=\"highlight\">{0}</span>", sKeyword);
    }

    for (int i = totalCount - 1; i >= 0; i--)
    {
        input = Regex.Replace(input, "\\~" + i + "\\~", sHighlights[i], RegexOptions.IgnoreCase);
    }

    return input;
}