Ruby方式：按零划分

Question

我有以下方法来计算平均值：

def compute_average(a,b,c,d,e)
  total = [a,b,c,d,e].sum.to_f
  average = [a, 2*b, 3*c, 4*d, 5*e].sum / total
  average.round(2)
end

这没什么特别的，但它有一个问题，我希望所有平均方程都有：如果输入全部为零，它可能除以零。

所以，我想到了这样做：

def compute_average(a,b,c,d,e)
  total = [a,b,c,d,e].sum.to_f
  if total==0
    average = 0.00
  else
    average = [a, 2*b, 3*c, 4*d, 5*e].sum / total
    average.round(2)
  end
end

......这有效，但对我来说感觉很糟糕。是否有更优雅的“Ruby Way”来避免这种划分为零的问题？

我希望我拥有的是“除非那么”的操作员，比如......

average = numerator / denominator unless denominator == 0 then 0

有什么建议吗？

Answer 1

您可以使用nonzero?，如：

def compute_average(a,b,c,d,e)
  total = [a,b,c,d,e].sum.to_f
  average = [a, 2*b, 3*c, 4*d, 5*e].sum / (total.nonzero? || 1)
end

更多人会更熟悉使用三元运算符(total == 0 ? 1 : total)，这是另一种可能性。

Answer 2

通常依靠rescue捕获异常，然后返回默认值：

def compute_average(a, b, c, d, e)
  total = [a, b, c, d, e].sum.to_f
  average = [ a, 2*b, 3*c, 4*d, 5*e ].sum / total
  average.round(2)
  rescue ZeroDivisionError
    0.0
end

我也会写：

average = numerator / denominator unless denominator == 0 then 0

作为

average = (denominator == 0) ? 0 : numerator / denominator

Answer 3

虽然这是一个过时的主题，但我认为我会使用一个简单的衬垫，你可以使用......

@average = variable1 / variable2 rescue 0

Answer 4

对我而言，最干净的方式是：

numerator / denominator rescue 0

它还可以帮助您避免处理0 / 0。

正如@Andrew所指出的，这仅对整数有效。有关详细信息，请参阅此答案的评论。

Answer 5

def compute_average(a,b,c,d,e)
  total = (a+b+c+d+e).to_f
  total.zero? ? 0 : ((a + 2*b + 3*c + 4*d + 5*e) / total).round(2)
end

Answer 6

TL; DR：一种可能的解决方案

def compute_average(*values)

  # This makes sure arrays get flattened to a single array.
  values.flatten!

  # Throws away all nil values passed as arguments.
  values.reject!(&:nil?)

  # Throws away all non-numeric values.
  # This includes trashing strings that look like numbers, like "12".
  values.keep_if{ |v| v.is_a? Numeric }

  total = values.sum.to_f
  return Float::NAN if total.zero?

  # I'm not sure what this business is
  #   average = [a, 2*b, 3*c, 4*d, 5*e].sum / total
  # but it can be translated to
  average = values.each_with_index.map{ |v,i| v*(i+1) }.sum / total

  average.round(2)
end

这可以防止所有情况：

compute_average(1,2,3,4,5)
=> 3.67

compute_average(0,0,0,0,0)
=> NaN

compute_average(1,2,nil,4,5)
=> 3.08

compute_average(1,2,"string",4,5)
=> 3.08

compute_average(1)
=> 1.0

compute_average([1,2,3,4,5])
=> 3.67

compute_average
=> NaN

原始功能：

def compute_average(a,b,c,d,e)
  total = [a,b,c,d,e].sum.to_f
  average = [a, 2*b, 3*c, 4*d, 5*e].sum / total
  average.round(2)
end

考虑检查零：

def compute_average(a,b,c,d,e)
  total = [a,b,c,d,e].sum.to_f
  return if total.zero?
  average = [a, 2*b, 3*c, 4*d, 5*e].sum / total
  average.round(2)
end

此更改仅针对一种情况进行保护：

compute_average(1,2,3,4,5)
# => 3.67

compute_average(0,0,0,0,0)
# => nil

compute_average(1,2,nil,4,5)
# => TypeError: NilClass can't be coerced into Fixnum

compute_average(1,2,"string",4,5)
# => TypeError: String can't be coerced into Fixnum

compute_average(1)
# => ArgumentError: wrong number of arguments calling `compute_average` (1 for 5)

compute_average([1,2,3,4,5])
# => ArgumentError: wrong number of arguments calling `compute_average` (1 for 5)

compute_average
# => ArgumentError: wrong number of arguments calling `compute_average` (0 for 5)

考虑使用内联rescue

def compute_average(a,b,c,d,e)
  total = [a,b,c,d,e].sum.to_f
  average = [a, 2*b, 3*c, 4*d, 5*e].sum / total rescue 0
  average.round(2)
end

此更改仅针对一个案例进行了保护：

compute_average(1,2,3,4,5)
# => 3.67

compute_average(0,0,0,0,0)
# => NaN

compute_average(1,2,nil,4,5)
# => TypeError: NilClass can't be coerced into Fixnum

compute_average(1,2,"string",4,5)
# => TypeError: String can't be coerced into Fixnum

compute_average(1)
# => ArgumentError: wrong number of arguments calling `compute_average` (1 for 5)

compute_average([1,2,3,4,5])
# => ArgumentError: wrong number of arguments calling `compute_average` (1 for 5)

compute_average
# => ArgumentError: wrong number of arguments calling `compute_average` (0 for 5)

使用内联rescue会产生另一种后果。考虑一下这个错字：

def compute_average(a,b,c,d,e)
  total = [a,b,c,d,e].sum.to_f
  average = [a, 2*b, 3*c, 4*d, 5*e].smu / total rescue 0
  #                                 ^^^
  average.round(2)
end

compute_average(1,2,3,4,5)
# => 0.0

compute_average(0,0,0,0,0)
# => 0.0

考虑使用rescue

def compute_average(a,b,c,d,e)
  total = [a,b,c,d,e].sum.to_f
  average = [a, 2*b, 3*c, 4*d, 5*e].sum / total
  average.round(2)
rescue ZeroDivisionError
  0.0
end

这样做更好，因为它不会隐藏错误，但可以防止与上面的rescue相同的情况。

我称之为正常平均值计算的另一个版本

作为旁注，我熟悉的平均操作是使用总数/计数来计算的，所以这是一个版本。

def compute_average(*values)

  # This makes sure arrays get flattened to a single array.
  values.flatten!

  # Throws away all nil values passed as arguments.
  values.reject!(&:nil?)

  # Throws away all non-numeric values.
  # This includes trashing strings that look like numbers, like "12".
  values.keep_if{ |v| v.is_a? Numeric }

  total = values.sum.to_f
  count = values.count
  return Float::NAN if count.zero?

  total / count
end

这可以防止所有情况：

compute_average(1,2,3,4,5)
=> 3.0

compute_average(0,0,0,0,0)
=> 0.0

compute_average(1,2,nil,4,5)
=> 3.0

compute_average(1,2,"string",4,5)
=> 3.0

compute_average(1)
=> 1.0

compute_average([1,2,3,4,5])
=> 3.0

compute_average
=> NaN

Answer 7

我不是一个Ruby-ist，但我会这样做：

average = denominator.nonzero? ? numerator/denominator : 0

可能有更好的答案，但这可能就足够了。

Answer 8

如果要分割的数字或分母是浮点数，

/不会返回零分割错误。

def compute_average(a,b,c,d,e)
  total = [a,b,c,d,e].sum.to_f
  average = [a, 2*b, 3*c, 4*d, 5*e].sum / total
  average.finite? ? average.round(2) : 0.0
end

更一般地说，在ruby1.9下，

def compute_average *args
  average = args.to_enum.with_index.map{|x, w| x * w}.sum / args.sum.to_f
  average.finite? ? average.round(2) : 0.0
end