I've got an array of hashes and would like to sum up selected values. I know how to sum all of them or one of them but not how to select more than one key.
ie:
[{"a"=>5, "b"=>10, "active"=>"yes"}, {"a"=>5, "b"=>10, "active"=>"no"}, {"a"=>5, "b"=>10, "action"=>"yes"}]
To sum all of them I using:
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'
To sum one key, I do:
h.map{|x| x['a']}.reduce(:+)
=> 15
How do I go about summing up values for keys 'a' and 'b'?
You can use 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]
If all required keys have values it will be shorter:
hs.map { |h| h.values_at(*keys) }.inject { |a, v| a.zip(v).map(&:sum) }
# => [3, 6]
If you want Hash
back:
Hash[keys.zip(hs.map { |h| h.values_at(*keys) }.inject{ |a, v| a.zip(v).map(&:sum) })]
# => {:a => 3, :b => 6}
I'd do something like this:
a.map { |h| h.values_at("a", "b") }.transpose.map { |v| v.inject(:+) }
#=> [15, 30]
Step by step:
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]
How is this ?
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}
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