Indexing

Index.cs

public static class SearchEx
{
	public static IList<string> NGrams( string sentence, int q)
	{
		int total = sentence.Length - q;
		List<string> tokens = new List<string>();
		for (int i = 0; i <= total; i++)
			tokens.Add(sentence.Substring(i, q));
		return tokens;
	}
	public static Dictionary<string, List<T>> ToIndex<T>
	(
	 //The collection on which the indexing has to be performed
         this IEnumerable<T> objects, 
         //The property which should be used to generate the indexing keys
	 string indexOn, 
	 //Size of the key to be used as indices in the index. 
	 //Should have a default value. But I shall leave it up to you
	 int keySize, 
	 //Should the keys be agnostic of the case ? 
	 //By default they are
	 bool ignoreCase = true) where T : class
	{
		Dictionary<string, List<T>> index = new Dictionary<string, List<T>>();		
		var projections = o
		bjects.Select(item => 
		new 
		  { 
		     Toks = NGrams(
		 	     typeof(T).GetProperty(indexOn)
		                      .GetValue(item)
		                     .ToString(),
		                     keySize), 
		     ItemItself = item 
		  });
		foreach (var proj in projections)
		{
		  foreach (var tok in proj.Toks)
			if (!index.ContainsKey(tok))
		   	  index.Add(tok, new List<T>() { proj.ItemItself});
			else 
			  index[tok].Add(proj.ItemItself);
		}
		return index;
	}
}