[ruby-core:62420] [ruby-trunk - Feature #9808] [Open] Enumerable#argmin_by, #argmax_by

Issue #9808 has been reported by Ilya Vorontsov.

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

* Author: Ilya Vorontsov
* Status: Open
* 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:


(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):

# 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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