>我有一个哈希数组,想总结选定的值。我知道如何对所有这些或其中一个求和,但不知道如何选择多个键。
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'
为了总结一个键,我做到了:
h.map{|x| x['a']}.reduce(:+)
=> 15
如何对键"a"和"b"的值求和?
您可以使用
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]
如果您想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}
我会做这样的事情:
a.map { |h| h.values_at("a", "b") }.transpose.map { |v| v.inject(:+) }
#=> [15, 30]
循序渐进:
a.map { |h| h.values_at("a", "b") } #=> [[5, 10], [5, 10], [5, 10]]
.transpose #=> [[5, 5, 5], [10, 10, 10]]
.map { |v| v.inject(:+) } #=> [15, 30]
这是怎么回事?
h = [{"a"=>5, "b"=>10, "active"=>"yes"}, {"a"=>5, "b"=>10, "active"=>"no"}, {"a"=>5, "b"=>10, "action"=>"yes"}]
p h.map{|e| e.reject{|k,v| %w(active action).include? k } }.inject{|memo, el| memo.merge( el ){|k, old_v, new_v| old_v + new_v}}
# >> {"a"=>15, "b"=>30}