Group hashes by keys and sum the values

Question

I have an array of hashes:

[{\"Vegetable\"=>10}, {\"Vegetable\"=>5}, {\"Dry Goods\"=>3>}, {\"Dry Goods\"=>2}]

I need to use

Answer 1

ar = [{"Vegetable"=>10}, {"Vegetable"=>5}, {"Dry Goods"=>3}, {"Dry Goods"=>2}]
p ar.inject{|memo, el| memo.merge( el ){|k, old_v, new_v| old_v + new_v}}
#=> {"Vegetable"=>15, "Dry Goods"=>5}

Hash.merge with a block runs the block when it finds a duplicate; inject without a initial memo treats the first element of the array as memo, which is fine here.