Ruby:Sum选择哈希值

Question

我有一系列哈希值,想总结选定的值.我知道如何总结所有这些或其中一个而不是如何选择多个键.

即:

[{"a"=>5, "b"=>10, "active"=>"yes"}, {"a"=>5, "b"=>10, "active"=>"no"}, {"a"=>5, "b"=>10, "action"=>"yes"}] 

为了总结所有这些,我使用:

t = h.inject{|memo, el| memo.merge( el ){|k, old_v, new_v| old_v + new_v}}
=> {"a"=>15, "b"=>30, "active"=>"yesnoyes"} # I do not want 'active'

总结一把钥匙,我做:

h.map{|x| x['a']}.reduce(:+)
=> 15 

如何总结键'a'和'b'的值？

Answer 1

你可以使用values_at:

hs = [{:a => 1, :b => 2, :c => ""}, {:a => 2, :b => 4, :c => ""}]
keys = [:a, :b]
hs.map { |h| h.values_at(*keys) }.inject { |a, v| a.zip(v).map { |xy| xy.compact.sum }}
# => [3, 6]

如果所有必需的键都有值,它将更短:

hs.map { |h| h.values_at(*keys) }.inject { |a, v| a.zip(v).map(&:sum) }
# => [3, 6]

如果你想Hash回来:

Hash[keys.zip(hs.map { |h| h.values_at(*keys) }.inject{ |a, v| a.zip(v).map(&:sum) })]
# => {:a => 3, :b => 6}