c# - What is faster in finding element with property of maximum value

Question

Commonly, to find element with property of max value I do like this

var itemWithMaxPropValue = collection.OrderByDescending(x => x.Property).First();

But is it good way from performance point of view? Maybe I should do something like this?

var maxValOfProperty = collection.Max(x => x.Property);
var itemWithMaxPropValue = collection
                                 .Where(x => x.Property == maxValueOfProperty).First();

Answer 1

Sorting is N * log (N) while Max has N only time complexity, so Max is faster. What you're looking for is ArgMax function which Linq doesn't provide, so I suggest implementing it, e.g:

  public static class EnumerableExtensions {
    public static T ArgMax<T, K>(this IEnumerable<T> source, 
                                 Func<T, K> map, 
                                 IComparer<K> comparer = null) {
      if (Object.ReferenceEquals(null, source))
        throw new ArgumentNullException("source");
      else if (Object.ReferenceEquals(null, map))
        throw new ArgumentNullException("map");

      T result = default(T);
      K maxKey = default(K);
      Boolean first = true;

      if (null == comparer)
        comparer = Comparer<K>.Default;

      foreach (var item in source) {
        K key = map(item);

        if (first || comparer.Compare(key, maxKey) > 0) {
          first = false;
          maxKey = key;
          result = item;
        }
      }

      if (!first)
        return result;
      else
        throw new ArgumentException("Can't compute ArgMax on empty sequence.", "source");
    }
  }

So you can put it simply

  var itemWithMaxPropValue = collection
    .ArgMax(x => x.Property);