如何找到数组最大值的索引？

Question

我尝试了这里推荐的解决方案 -- In Ruby, what is the cleanest way of obtaining the index of the largest value in an array?

array = [nil, nil, nil, nil, nil, 0.9655172413793104, nil, nil]
idx = array.each_with_index.max[1]

但我遇到了一些例外情况：

ArgumentError: comparison of Array with Array failed
    from (irb):4:in `each'
    from (irb):4:in `each_with_index'
    from (irb):4:in `each'
    from (irb):4:in `max'
    from (irb):4
    from /Users/davea/.rvm/gems/ruby-2.4.0/gems/railties-5.0.3/lib/rails/commands/console.rb:65:in `start'
    from /Users/davea/.rvm/gems/ruby-2.4.0/gems/railties-5.0.3/lib/rails/commands/console_helper.rb:9:in `start'
    from /Users/davea/.rvm/gems/ruby-2.4.0/gems/railties-5.0.3/lib/rails/commands/commands_tasks.rb:78:in `console'
    from /Users/davea/.rvm/gems/ruby-2.4.0/gems/railties-5.0.3/lib/rails/commands/commands_tasks.rb:49:in `run_command!'
    from /Users/davea/.rvm/gems/ruby-2.4.0/gems/railties-5.0.3/lib/rails/commands.rb:18:in `<top (required)>'
    from bin/rails:4:in `require'
    from bin/rails:4:in `<main>'

Answer 1

如果你想从结果中省略nils，那么你可以使用：

array.index(array.compact.max)

或者如果您希望将 nils 视为零，则首先将它们转换为 Floats：

array.index(array.map(&:to_f).max)

如果出现平局，这将 return 第一个 最大值的索引。您还可以使用 Array#rindex.

获取 last 索引

Answer 2

def max_idx(array)
  mx = array.select { |e| e.kind_of?(Numeric) }.max 
  mx ? array.each_index.select { |i| array[i] == mx } : nil
end      

require 'bigdecimal'
max_idx [nil,3,1]                   #=> [1]
max_idx [nil,3.2,"cat",1]           #=> [1]
max_idx [nil,3,nil,1,3]             #=> [1,4]
max_idx [nil,3.2,nil,1,3.2]         #=> [1,4]
max_idx [nil,Rational(3),1]         #=> [1]
max_idx [nil,BigDecimal.new("3"),1] #=> [1]
max_idx [nil,nil,nil]               #=> nil

如何找到数组最大值的索引？

How do I find the index of the maximum value of an array?

ruby

arrays

max

ruby-2.4