argmax and argmin (or max_by and min_by)

[DartBot]

This issue was originally filed by [email protected]

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Link to StackOverflow question:
http://stackoverflow.com/questions/13884666/any-max-and-argmax

I would like Collection#argmax and argmin. Examples of where these might be useful:
final animalNames = ['cat', 'turtle', 'sheep'];
final longest = animalNames.argmax((name) => name.length);
// longest == 'turtle'

final leastHealth = monsters.argmin((monster) => monster.health);

These are the same as Ruby max_by and min_by:
http://ruby-doc.org/core-1.9.3/Enumerable.html#method-i-max_by
They are also very commonly used in mathematics:
http://en.wikipedia.org/wiki/Arg_max

[iposva-google]

Removed Type-Defect label.
Added Type-Enhancement, Area-Library, Triaged labels.

[DartBot]

This comment was originally written by @seaneagan

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this is very similar to issue #1319

[DartBot]

This comment was originally written by [email protected]

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I think you might be right. They should be merged. The lack of examples and my misunderstanding of what happens when max has no parameters confused me. Are the following examples correct:
[1, 2, 3].max(); // -> 3
[1, 2, 3].max((e) => (e == 2) ? 4 : e); // -> 2
['cat', 'monkey', 'sheep'].max(); // -> sheep
['cat', 'monkey', 'sheep'].max((e) => e.length); // -> 'monkey'
monsters.max() // -> depends on what > is overloaded to mean
monsters.max((e) => e.health); // -> monster with most health

Is it that [1, 2, 3].max() returns a value (3) but [1, 2, 3].max((e) => (e == 2) ? 4 : e) returns the argument that mapped to the highest value?

[lrhn]

I don't think we want a specific argmin/argsort that works direcly given a projection function, but I do think we should have min/max on Iterable, and possibly a helper for creating comparison functions from projections so you can write:

  list.min(Comparable.compareBy((m) => m.health))

which would be equivalent to

  list.min((a, b) => a.health.compareTo(b.health))

which would find the element in list with the lowest health.

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Added Duplicate label.
Marked as being merged into #1319.