using System;

using System.Collections.Generic;

using System.Linq;

​

public class Program

{

    public static void Main()

    {

        var ids = Enumerable.Range(1, 1261).ToList();

        var weights = Enumerable.Range(1, 1261).Select(x => (double)x).ToList();

        var result = zipIt(ids, weights);

        Console.WriteLine(result.Count);

    }

    static private Dictionary<int, double> zipIt(List<int> ids, List<double> weights)

    {

        // OutOfMemoryException thrown at this line:

        var result = ids.Zip(weights, (x, y) => new { x, y })

            .ToDictionary(_ => _.x, _ => _.y);

        return result;

    }

}