CODEWITHSUNDEEP
c#linqcollectionscomparisonmax
Daniel T.
Daniel T.

Reputation: 38400

What's the simplest way of returning the larger of two numbers?

Let's say I have an entity that looks like this:

public class Album()
{
    public DateTime LastUpdated { get; set; }
    public List<Picture> Pictures { get; set; }
}

What I want to do is create a LastActivity property that will return the latest date of the activity. This is easy enough for the Pictures collection:

public DateTime LastActivity
{
    get { return Pictures.Max(x => x.LastUpdated); }
}

However, I also want to consider the LastUpdated property on the Album entity as well. I could use this code:

public DateTime LastActivity
{
    get { return Pictures.Max(x => x.LastUpdated) > this.LastUpdated
              ? Pictures.Max(x => x.LastUpdated)
              : this.LastUpdated) };
}

But this is bad because it will do the Max() transformation twice. Is there a better way of writing this code?

Answer

This is the solution I came up with, based on the accepted answer:

public virtual DateTime LastActivity
{
    get
    {
        var max = Pictures.Any() ? Pictures.Max(x => x.LastUpdated) : DateTime.MinValue;
        return max > this.LastUpdated ? max : this.LastUpdated;
    }
}

The thing to watch out for is that if you do a Max() on an empty collection, you'll get an exception, so you have to check to see if there's anything in the collection first.

Upvotes: 3

Views: 5383

Answers (9)

LukeH
LukeH

Reputation: 269398

This is fairly straightforward and should take an empty Pictures collection in its stride:

public DateTime LastActivity
{
    get
    {
        return Pictures.Aggregate(LastUpdated,
                            (a, x) => x.LastUpdated > a ? x.LastUpdated : a);
    }
}

Upvotes: 0

Dan J
Dan J

Reputation: 16708

To keep it LINQy...

public DateTime LastActivity
{
    get 
    { 
         return Pictures.Any(x => x.LastUpdated > this.LastUpdated) 
                ? Pictures.Max(x => x.LastUpdated) 
                : this.LastUpdated; 
    }
}

Update(s): added the default LastUpdated to be returned if the LINQ expression returns no results, and corrected for the OP's comment.

Upvotes: 0

Rohan West
Rohan West

Reputation: 9298

Just store the max in a variable rather that performing the calculation twice.

public DateTime LastActivity
{
    get 
    { 
        var max = Pictures.Max(x => x.LastUpdated);
        return max > this.LastUpdated
          ? max
          : this.LastUpdated 
    };
}

Upvotes: 7

Albin Sunnanbo
Albin Sunnanbo

Reputation: 47048

public DateTime LastActivity
{         
    get { return Pictures.Select(x => x.LastUpdated).Concat(new DateTime[] { this.LastUpdated }).Max();
}

Upvotes: 1

Platinum Azure
Platinum Azure

Reputation: 46193

Just store the max value in a temporary:

public DateTime LastActivity
{
    get {
        DateTime maxLastUpdated = Pictures.Max(x => x.LastUpdated);
        return maxLastUpdated > this.LastUpdated
            ? maxLastUpdated
            : this.LastUpdated) };
}

Upvotes: 0

Jeffrey L Whitledge
Jeffrey L Whitledge

Reputation: 59463

How about this?

public DateTime LastActivity 
{ 
    get 
    {
         DateTime lastPicture = Pictures.Max(x => x.LastUpdated);
         return lastPicture > this.LastUpdated ? lastPicture : this.LastUpdated;
     }
}

Upvotes: 1

mlibby
mlibby

Reputation: 6734

public DateTime LastActivity
{
    get
    {
        var picturesMax = Pictures.Max(x => x.LastUpdated);
        return picturesMax > this.LastUpdated
          ? picturesMax
          : this.LastUpdated)
    };
}

Upvotes: 1

Charles Bretana
Charles Bretana

Reputation: 146499

I use the following in a framework library...

public static T Maximum<T>(params T[] values) 
    where T : struct, IComparable<T>
{
    var rV = values[0];
    foreach (var v in values.Where
        (v => v.CompareTo(rV) > 0))
        rV = v;
    return rV;
}

In client code I can simply write

var maxVal = lib.Maximum(Value1, Value2, .... , ValueN);

Upvotes: 0

Don Kirkby
Don Kirkby

Reputation: 56660

Just assign the picture dates maximum to a local variable and then do the comparison you've already written.

Upvotes: 2

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