Ravendb how to use Map Reducer

I have a 3-column table Id, Title, Section.

1. I want a unique value from the title column. ( which I fetch by Map Reduce index)
2. Now the user will select Title from the dropdown then want to fetch the Unique section which will match by Title (How to fetch unique section which match Title. I use Distinct but performance get down)
3. Then the user will select the Section where I want to fetch Unique Title by matching the title and section

My Index

 class UniqueActIndex : AbstractIndexCreationTask<ActRuleModel, UniqueActIndex.Result> {
    public class Result {
        public string ActTitle { get; set; }
    }

    public UniqueActIndex() {
        Map = orders => from o in orders
                        select new Result {
                            ActTitle = Regex.Replace(o.ActTitle, @"[^0-9a-zA-Z]+", " ")
                        };

        Reduce = results => from r in results
                            group r by r.ActTitle into g
                            select new Result {
                                ActTitle = g.Key
                            };



    }
}

}