WeightedSearch.cs

using System;
using System.Collections.Generic;
using System.Linq;

namespace dk.odense.EnPlan.Utils
{
    public class WeightedSearch<TValue>
    {
        private readonly List<TValue> _list;
        private readonly List<Func<TValue, string, int>> _weights = new List<Func<TValue, string, int>>();

        public WeightedSearch(List<TValue> list)
        {
            _list = list;
        }

        public WeightedSearch<TValue> AddWeight(Func<TValue, string, int> weight)
        {
            _weights.Add(weight);

            return this;
        }

        public IEnumerable<TValue> Search(string[] tokens)
        {
            // Apply weights
            var weighted = _list.Select(value => new
            {
                Value = value,
                Weight =
                    tokens.Aggregate(0, (tokenTotal, token) => tokenTotal + _weights.Aggregate(0, (weightTotal, weight) => weightTotal + weight(value, token)))
            });

            // Order by weight
            var ordered = weighted.OrderByDescending(arg => arg.Weight);

            // Return the actual values
            return ordered.Select(arg => arg.Value).ToList();
        }

        public IEnumerable<TValue> SearchOptimized(List<string> tokens)
        {
            var weigthed = new List<WeightedValue<TValue>>();

            foreach (var element in _list)
            {
                var weigthedValue = new WeightedValue<TValue>()
                {
                    Value = element,
                    Weight = 0
                };

                foreach (var token in tokens)
                {
                    foreach (Func<TValue, string, int> t in _weights)
                    {
                        weigthedValue.Weight += t(element, token);
                    }
                }

                weigthed.Add(weigthedValue);
            }

            return weigthed.Select(value => value.Value).ToList();
        } 
    }

    class WeightedValue<TValue>
    {
        public TValue Value { get; set; }
        public int Weight { get; set; }
    }
}