Question

I’m searching through a generic list (or IQueryable) which contains 3 columns. I’m trying to find the value of the 3 column, based on 1 and 2, but the search is really slow. For a single search, the speed isn’t noticeable, but I’m performing this search on a loop, and for 700 iterations, it takes a combined time of over 2 minutes, which isn’t any use. Columns 1 and 2 are int and column 3 is a double. Here is the linq I’m using:

public static Distance FindByStartAndEnd(int start, int end, IQueryable<Distance> distanceList)
{
    Distance item = distanceList.Where(h => h.Start == start && h.End == end).FirstOrDefault();
    return item ;
}

There could be up do 60,000 entries in the IQueryable list. I know that is quite a lot, but I didn’t think it would pose any problem for searching.

So my question is, is there a better way to search through a collection when needing to match 2 columns to get value of a third? I guess I need all 700 searches to be almost instant, but it takes about 300ms for each which soon mounts up.

UPDATE – Final Solution #######################

I’ve now created a dictionary using Tuple with start and end as the key. I think this could be the right solution.

var dictionary = new Dictionary<Tuple<int, int>, double>();

var key = new Tuple<int, int>(Convert.ToInt32(reader[0]), Convert.ToInt32(reader[1]));
var value = Convert.ToDouble(reader[2]);

if (value <= distance)
{
    dictionary.Add(key, value);
}
var key = new Tuple<int, int>(5, 20);

Works fine – much faster

Answer 1

Create a dictionary where columns 1 and 2 create the key. You create the dictionary once and then your searches will be almost instant.