更新哈希值

Question

我正在尝试将值减去三后更新哈希值。例如，

extinct_animals = {
  "Passenger Pigeon" => 1914,
  "Tasmanian Tiger" => 1936,
  "Eastern Hare Wallaby" => 1890,
  "Dodo" => 1662,
  "Pyrenean Ibex" => 2000,
  "West African Black Rhinoceros" => 2011,
  "Laysan Crake" => 1923
}

我有这段代码，它将值减去三：

extinct_animals.each {|animal, year| puts year - 3}

和输出：

1911
1933
1887
1659
1920

如何返回带有键和新值的整个哈希？

Answer 1

您将要使用Hash#transform_values!，它在MRI v2.4中首次亮相：

extinct_animals.transform_values! { |v| v - 3 }
  #=> {"Passenger Pigeon"=>1911, "Tasmanian Tiger"=>1933,
  #    "Eastern Hare Wallaby"=>1887, "Dodo"=>1659, "Pyrenean Ibex"=>1997,
  #    "West African Black Rhinoceros"=>2008, "Laysan Crake"=>1920}

extinct_animals
  #=> {"Passenger Pigeon"=>1911, "Tasmanian Tiger"=>1933,
  #    "Eastern Hare Wallaby"=>1887, "Dodo"=>1659, "Pyrenean Ibex"=>1997,
  #    "West African Black Rhinoceros"=>2008, "Laysan Crake"=>1920}

Answer 2

在该块内，确保您正在使用=修改哈希：

extinct_animals.each { |animal, year| extinct_animals[animal] = year - 3 }
=> {
  "Passenger Pigeon" => 1911,
  "Tasmanian Tiger" => 1933,
  "Eastern Hare Wallaby" => 1887,
  "Dodo" => 1659,
  "Pyrenean Ibex" => 1997,
  "West African Black Rhinoceros" => 2008,
  "Laysan Crake" => 1920
}

请勿使用puts。只是写到控制台。

此解决方案的更简短版本为：

extinct_animals.each { |animal, _year| extinct_animals[animal] -= 3 }

我们在year前面加一个下划线，以指示该变量未在块内使用。