C# Finding relevant document snippets for search result display

Question

In developing search for a site I am building, I decided to go the cheap and quick way and use Microsoft Sql Server\'s Full Text Search engine instead of something more robust l

Answer 1

public class Highlighter
{        
    private class Packet
    {
        public string Sentence;
        public double Density;
        public int Offset;
    }

    public static string FindSnippet(string text, string query, int maxLength)
    {
        if (maxLength < 0)
        {
            throw new ArgumentException("maxLength");
        }
        var words = query.Split(' ').Where(w => !string.IsNullOrWhiteSpace(w)).Select(word => word.ToLower()).ToLookup(s => s);             
        var sentences = text.Split('.');
        var i = 0;
        var packets = sentences.Select(sentence => new Packet 
        { 
            Sentence = sentence, 
            Density = ComputeDensity(words, sentence),
            Offset = i++
        }).OrderByDescending(packet => packet.Density);
        var list = new SortedList();            
        int length = 0;                
        foreach (var packet in packets)
        {
            if (length >= maxLength || packet.Density == 0)
            {
                break;
            }
            string sentence = packet.Sentence;
            list.Add(packet.Offset, sentence.Substring(0, Math.Min(sentence.Length, maxLength - length)));
            length += packet.Sentence.Length;
        }
        var sb = new List();
        int previous = -1;
        foreach (var item in list)
        {
            var offset = item.Key;
            var sentence = item.Value;
            if (previous != -1 && offset - previous != 1)
            {
                sb.Add(".");
            }
            previous = offset;             
            sb.Add(Highlight(sentence, words));                
        }
        return String.Join(".", sb);
    }

    private static string Highlight(string sentence, ILookup words)
    {
        var sb = new List();
        var ff = true;
        foreach (var word in sentence.Split(' '))
        {
            var token = word.ToLower();
            if (ff && words.Contains(token))
            {
                sb.Add("[[HIGHLIGHT]]");
                ff = !ff;
            }
            if (!ff && !string.IsNullOrWhiteSpace(token) && !words.Contains(token))
            {
                sb.Add("[[ENDHIGHLIGHT]]");
                ff = !ff;
            }
            sb.Add(word);
        }
        if (!ff)
        {
            sb.Add("[[ENDHIGHLIGHT]]");
        }
        return String.Join(" ", sb);
    }

    private static double ComputeDensity(ILookup words, string sentence)
    {            
        if (string.IsNullOrEmpty(sentence) || words.Count == 0)
        {
            return 0;
        }
        int numerator = 0;
        int denominator = 0;
        foreach(var word in sentence.Split(' ').Select(w => w.ToLower()))
        {
            if (words.Contains(word))
            {
                numerator++;
            }
            denominator++;
        }
        if (denominator != 0)
        {
            return (double)numerator / denominator;
        }
        else
        {
            return 0;
        }
    }
}

Example:

highlight "Optic flow is defined as the change of structured light in the image, e.g. on the retina or the camera’s sensor, due to a relative motion between the eyeball or camera and the scene. Further definitions from the literature highlight different properties of optic flow" "optic flow"

Output:

[[HIGHLIGHT]] Optic flow [[ENDHIGHLIGHT]] is defined as the change of structured light in the image, e... Further definitions from the literature highlight diff erent properties of [[HIGHLIGHT]] optic flow [[ENDHIGHLIGHT]]