Ndtyjky

I have a method which I call CalculatePopularityScore. It exists on a Story object. The Story object has a field which is an ICollection of Comment objects.

public virtual ICollection<Comment> Comments { get; set; }

The Comment object has another collection of Reply objects.

My method looks at the story, loops through the comments associated with that story, and if the story's comments has replies, adds up that total. That, along with some other fields, gives me a very (and I stress this) very rudimentary algorithm of a story's popularity.

public double CalculateStoryPopularityScore()

{

            if (Comments == null) throw new ArgumentException("Comments can't be null");

            if (Comments.Count < 0) throw new ArgumentException("Comments can't be less than zero.");



            int ReplyCountSum = 0;

            double ReplyScore;

            double CommentScore;

            double InsightfulVoteScore;

            double UsefulVoteScore;

            double viewCount;



            foreach (var comment in Comments)

            {

                int replyCount;



                if (comment.Replies == null)

                {

                    throw new ArgumentNullException("Replies cannot be null");

                }



                if (comment.Replies.Count() == 0)

                {

                    replyCount = 0;

                } else

                {

                    replyCount = comment.Replies.Count();

                }



                ReplyCountSum += replyCount;

            }



            ReplyScore = ReplyCountSum * 4;

            CommentScore = Comments.Count() * 4;

            InsightfulVoteScore = InsightFulVoteCount * 3;

            UsefulVoteScore = UsefulVoteCount * 2;

            viewCount = ViewCount;



            double PopularityScore = CommentScore + ReplyScore + InsightfulVoteScore + + UsefulVoteScore + viewCount;

            return PopularityScore;

}

This seems to work fine. Now, what I'd like to do is take this method and apply it to a number of stories (i.e. a list).

I currently have this method written. It has not yet implemented another loop to look through the replies to the comments collection of a story. I know nested loops are considered bad and slow. What would be the most efficient way to look at the list of stories, then the list of comments in each story, add up those replies, and calculate a story's popularity score?

public void CalculateStoryPopularityScore(List<Story> stories)

{

            if (stories == null) throw new ArgumentException("Stories can't be null");



            double CommentScore;

            double InsightfulVoteScore;

            double UsefulVoteScore;

            double PopularityScore;

            double ViewCount;



            foreach (var story in stories)

            {

                CommentScore = story.Comments.Count() * 4;

                InsightfulVoteScore = story.InsightFulVoteCount * 3;

                UsefulVoteScore = story.UsefulVoteCount * 2;

                ViewCount = story.ViewCount;



                PopularityScore = CommentScore + InsightfulVoteScore + UsefulVoteScore + ViewCount;

                story.PopularityScore = PopularityScore;

            }

}

Use SelectMany

var commentCount = story.Comments.Count();



// count all replies to all comments for a story

var replyCountSum = story.Comments

    .SelectMany(c => c.Replies)

    .Count();

Apply to a collection of stories:

stories.Select(s => new

{

    Story = s,

    CommentCount = s.Comments.Count(),

    ReplyCount = s.Comments.SelectMany(c => c.Replies).Count(),

});

Unless I'm missing something, all the scores you're calculating with a separate method can instead be written as a public read-only (calculated) property of the Story class. The reply count can be obtained by using SelectMany (which is used to flatten lists of lists into a single list) and then getting the Count property:

public class Story

{

    public List<Comment> Comments { get; set; }

    public int InsightFulVoteCount { get; set; }

    public int UsefulVoteCount { get; set; }

    public int ViewCount { get; set; }



    public int PopularityScore

    {

        get

        {

            return

                (Comments?.Count ?? 0) * 4 +

                (Comments?.SelectMany(comment => comment.Replies).Count() ?? 0) * 4 +

                InsightFulVoteCount * 3 +

                UsefulVoteCount * 2 +

                ViewCount;

        }

    }

}



public class Comment

{

    public List<string> Replies { get; set; }

}

In case you're not familiar with the null-conditional operator (?.), it returns null if the left operand (the object) is null before accessing the right operand (property or method of the object). If the left side is not null, then the property/method value is returned.

Then the null-coalescing operator (??) evaluates the left operand (which is the result of the property or method access) and, if it's null, it returns the right operand ('0' in our case).

Basically this simplifies the code. You don't have to do:

var score = 0;

if (Comments != null) score = Comments.Count;

You can just do:

var score = Comments?.Count ?? 0;