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[py2rb] sliceクラス

Last updated at Posted at 2021-12-14

はじめに

移植やってます。

slice (Python)

s = slice(0, 10, 3)
print(type(s))

a = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10][s]
# a = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10][s.start:s.stop:s.step]
print(a)

# <class 'slice'>
# [1, 4, 7, 10]

Pythonってsliceクラスがあるんですね。
3つの数値を持ったタプルなんだと思いますが。

どうする? (Ruby)

slice = Struct.new(:start, :stop, :step)
s = slice.new(0, 5, 3)
puts s
puts s.class
puts s.instance_of?(slice)

a = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10][s.start, s.stop]
print(a)

# #<struct start=0, stop=5, step=3>
# #<Class:0x000001e08c9f3260>
# true
# [1, 2, 3, 4, 5]

Structで代用できそうな気もします。
Sliceクラスを作る?

class Slice
  attr_reader :start, :stop, :step

  def initialize(start, stop, step)
    @start = start
    @stop = stop
    @step = step
  end

  def slice(array)
    @start = 0 if @start.nil?
    @stop = -1 if @stop.nil?
    if @step.nil?
      array[@start..@stop]
    else
      array[@start..@stop].select.with_index{ |num, i| i % @step == 0 }      
    end
  end
end

s = Slice.new(0, nil, 3)
puts s.class

a = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
print(s.slice a)

# Slice
# [1, 4, 7, 10]

メモ

  • Python の sliceクラス を学習した
  • 道のりは遠そう
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