How can I improve this sum with reduce method

Question

I would like to improve this sum using the reduce method, but I saw that works well for summing but also I have to do a subtract:

final = 0
@status.each do |data|
  final = final + data['pending_increase'] - data['pending_decrease']
end

The method I want to use is Enumerable#reduce

Answer 1

Something like this:

@status.reduce(0){|sum, data| sum + data['pending_increase'] - data['pending_decrease']}

or

@status.map{|data| data['pending_increase'] - data['pending_decrease']}.reduce(0, :+)

Answer 2

This will work too (as the initial seed is 0 ), but doesn't use reduce as requested

@status.sum{|data| data['pending_increase'] - data['pending_decrease']}

This two expressions are equivalent, being sum shorter and simpler than map / reduce

enum.sum{...} == enum.map{...}.reduce(0, :+)

Answer 3

如果这是在rails应用程序中，您可以这样做：

@status.map{|data| data['pending_increase'] - data['pending_decrease']}.sum

Answer 4

You could first compute the differences, then sum them:

@status.map { |data| data['pending_increase'] - data['pending_decrease'] }.reduce(:+)

but this has the disadvantage of creating a temporary array.

Just sayin'.