Select List item with max value using LINQ query

Question

I have List loadRecords where T type defines as follow

public class TransformerLoadRecord
{

    public double TotalLoadKva { get; set; }
    public double Total         


        

Answer 1

You need to sort (descending) the source list and take the first element:

var elementWithMaxKVA = loadRecords.OrderByDescending(l => l.TotalLoadKva).FirstOrDefault();

But this is not the fastest way, because OrderBy* will have to do more work than simply look up the max value.

You could instead implement your own extension method like that:

// error handling and argument checks ommitted for brevity
public static TSource MaxBy(this IEnumerable source, Func selector) where TComp : IComparable
{    
    using (var enumerator = source.GetEnumerator())
    {
        TSource max = default(TSource);
        TComp maxV = default(TComp);
        if (!enumerator.MoveNext()) return max; // or throw

        max = enumerator.Current;
        maxV = selector(max);

        while(enumerator.MoveNext())
        {
            TSource current = enumerator.Current;
            TComp currentV = selector(current);
            if (currentV.CompareTo(maxV) <= 0) continue;
            maxV = currentV;
            max = current;
        }

        return max;
    }
}

And use it like

var elementWithMaxKVA = loadRecords.MaxBy(l => l.TotalLoadKva);

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I think the MoreLinq nuget package already contains such a MaxBy method.