What's the C# equivalence of Python's min/max

Question

What's C#'s equivalence of the following Python's min/max code:

pairs = [ (2,"dog"), (1, "cat"), (3, "dragon"), (1, "tiger") ]

# Returns the PAIR (not the number) that minimizes on pair[0]
min_pair = min(pairs, key=lambda pair:pair[0])

# this will return (1, 'cat'), NOT 1

It seems that C#'s Enumerable.Min is very close. But according to its MSDN doc, it always returns the minimizing VALUE (not the original object). Am I missing anything?

EDIT

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Please note - I'm not inclined to achieve this by sorting first, since sorting (O(nlogn)) is computationally heavier than finding the minimum (O(n)).

Please also note - Dictionary is not a desired approach either. It cannot handle cases where there are duplicate keys - (1, "cat") and (1, "tiger").

More importantly, dictionary cannot handle cases where the items to be processed is a complex class. E.g., finding minimum over a list of animal objects, using age as the key:

class Animal
{
  public string name;
  public int age;
}

Answer 1

The BCL doesn't have a MinBy function, but it's easy to write one yourself.

public static T MinBy<T, C>(this IEnumerable<T> items, Func<T, C> projection) where C : IComparable<C> {
    return items.Aggregate((acc, e) => projection(acc).CompareTo(projection(e)) <= 0 ? acc : e);
}

You may choose to write a more complex MinBy than me, in order to avoid re-evaluating the projection. In any case, once you have your MinBy function you can easily solve the problem:

var pairs = new[] {Tuple.Create(2,"dog"), Tuple.Create(1, "cat"), Tuple.Create(3, "dragon"), Tuple.Create(1, "tiger")};
var min_pair = pairs.MinBy(e => e.Item1);

Answer 2

EDIT

var minage = collection.Min( x => x.Age ); //for maxage replace Min by Max
var minAgeAnimals = collection.where(x=> x.age == minage); 
foreach(Animal animal in minAgeAnimals )
   Console.Writeline (  animal.Age.ToString() + " : " + animal.Name); 

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Prev. Answered before edit of question

Make use of dictonary object in C# and than do something like this does the same thing you want

int minimumKey = touchDictionary.Keys.Min(); 
string value = "";
touchDictionary.TryGetValue(minimumKey, out value))
Console.Writeline ( "min key pair is:-" + minimumKey.ToString() + " : " + value); 

or

With the help of the linq its become to easy for you

var dictionary = new Dictionary<int, string>  
                     {{1, "one"}, {2, "two"}, {3, "three"}, {4, "four"}  };  

        var maxKey = dictionary.Max(x => x.Key);  
        var minkey = dictionary.Min(x => x.Key);  

Answer 3

Use

Dictionary<int, string> pairs = new Dictionary<int, string>()
                          { {2,"dog"}, {1, "cat"}, {3, "dragon"} };

var min = pairs.OrderBy(x => x.Key).FirstOrDefault();

OR

int min = pairs.Keys.Min();

Dictionary<int, string> result 
                          = new Dictionary<int, string>() { {min, pairs[min]} };

Answer 4

I would use

var min = pairs.OrderBy(x => x.FirstValue).FirstOrDefault();

and while I agree that sorting is heavier than finding the minimum value please note that this is not sorting the entire set. It is finding the first (or default) item in an ordered enumeration over the set - which is iterated lazily.

If you had

var min = pairs.OrderBy(x => x.FirstValue).ToList().FirstOrDefault();

then I'd agree - you are sorting your pairs and then taking the first. But LINQ is smarter than that, and you will not be sorting the set. You'll be taking the first from a potentially ordered but as yet unexecuted collection.

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In addition to your point about Dictionary being unable to use a complex collection - say a list of Animal - how would you sort by an Animal? You can never sort by a complex object. You instead need to use the age of the animal as the key. Dictionary can do this very easily - in fact, the key of a Dictionary would never be the same as the value of a Dictionary, else what would be the point?

var animals = new List<Animal>();
// get some animals...

var animalictionary = animals.ToDictionary(a => a.Age);
// assuming the animals have distinct ages, else

var animalLookup = animals.ToLookup(a => a.Age);

foreach (var animalGroup in animalLookup)
{
    var age = animalGroup.Key;
    Console.WriteLine("All these animals are " + age);
    foreach (Animal animal in animalGroup)
    {
        Console.WriteLine(animal.name);
    }
}