From: nobu@...
Date: 2014-05-06T14:40:35+00:00
Subject: [ruby-core:62424] [ruby-trunk - Feature #9808] [Feedback] Enumerable#argmin_by, #argmax_by

Issue #9808 has been updated by Nobuyoshi Nakada.

Description updated
Status changed from Open to Feedback

Could you explain what it does?

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Feature #9808: Enumerable#argmin_by, #argmax_by
https://bugs.ruby-lang.org/issues/9808#change-46573

* Author: Ilya Vorontsov
* Status: Feedback
* Priority: Normal
* Assignee: 
* Category: 
* Target version: 
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What about introducing `Enumerable` `#argmin_by` (and `#argmax_by` too, of course) method?
Use cases are wide from mathematical problems to a general tasks. Here are two very simple examples:

~~~ruby
(1..2).step(0.01).argmin_by{|x| Math.sin(x)*x}

queues = [[],[],[],[]]
# ...
least_busy_queue = queues.argmin_by{|queue| queues.size }
least_busy_queue << new_task
~~~

For cases when `#argmin_by` isn't enough because one need to obtain index of minimal element I suggest `#index_min_by` method which returns index of element for which block yields minimal value. It prevents user from using ineffective but straight two-pass algorithm like `arr.index(arr.min)`:

~~~ruby
# guess the number game
hidden_number = rand(100)
player_answers = 5.times.map{ gets.to_i }
best_player = player_answers.index_min_by{|answer| (answer-hidden_number).abs}
~~~



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