Question

Writing a sorting algorithm based off of Reddit’s here: http://amix.dk/blog/post/19588

I’m having a little trouble getting it all to fit together because some of the System.Math signatures differ in their application.

public class Calculation
{
    protected DateTime Epoch = new DateTime(1970,1,1);

    protected int EpochSeconds(DateTime date)
    {
        var td = date - Epoch;
        return td.Days*86400 + td.Seconds + ((td.Milliseconds)/1000000);
    }

    protected int Score(int upVotes,int downVotes)
    {
        return upVotes - downVotes;
    }

    public int HotScore(int upVotes,int downVotes,DateTime date)
    {
        var s = Score(upVotes, downVotes);
        var order = Math.Log(Math.Max(Math.Abs(s), 1), 10);
        var sign = Math.Sign(s); //Edit from Jonathon Reinhart
        var seconds = EpochSeconds(date) - 1134028003;
        return Math.Round(order + sign + *seconds/45000, 7);
    }
}

Edits for more information

Specifically I’m getting an error on the last line

return Math.Round(order + sign + *seconds/45000, 7);
//error "The * or -> operator must be applied to a pointer"

“

The closest match I can find in the method signature is this:
http://msdn.microsoft.com/en-us/library/f5898377

Answer 1

One recommendation I would make is to use Math.Sign(Int32). So:

var sign = new int();
if (s > 0) { sign = 1; }
else if (s < 0) { sign = -1; }
else { sign = 0; }

Becomes:

var sign = Math.Sign(s);

---

Ok, so you’re having problems with this line:

return Math.Round(order + sign + *seconds/45000, 7);

Well for one, you’re probably losing the fractional part in seconds/45000, because they are both int. Cast one to double first: ((double)seconds / 45000).

For two, you’ve likely got a syntactical error sign + *seconds. Do you mean + or *? It thinks you’re using seconds like a pointer.

Finally, Math.Round returns a double, but your HotScore method is returning an int. I’m guessing you want that to return a double.

My guess is that this is what you want:

public double HotScore(int upVotes,int downVotes,DateTime date)
{
    var score = Score(upVotes, downVotes);
    var order = Math.Log(Math.Max(Math.Abs(score), 1), 10);
    var sign = Math.Sign(score);
    var seconds = EpochSeconds(date) - 1134028003;
    return Math.Round(order + sign * ((double)seconds/45000), 7);
}

---

Also, I don’t think your EpochSeconds() is correct. I adapted this from here:

public long GetEpochTime(DateTime dt) 
{ 
    var ts = dt.Subtract(Convert.ToDateTime("1/1/1970 8:00:00 AM")); 

    return ((((((ts.Days * 24) + ts.Hours) * 60) + ts.Minutes) * 60) + ts.Seconds); 
}