红宝石嵌套数组中哈希键的总和

Question

I have an array containing arrays of hashes with identical sets of keys. I need to sum each set of keys for each array, leaving me with a single array of hashes.

array = [
  [{"x"=>"Apr, 2014", "price_rate"=>10, "cost_rate"=>10, "profit"=>10},
   {"x"=>"May, 2014", "price_rate"=>10, "cost_rate"=>10, "profit"=>10},
   {"x"=>"Jun, 2014", "price_rate"=>10, "cost_rate"=>10, "profit"=>10} ],
  [{"x"=>"Apr, 2014", "price_rate"=>10, "cost_rate"=>10, "profit"=>10},
   {"x"=>"May, 2014", "price_rate"=>10, "cost_rate"=>10, "profit"=>10},
   {"x"=>"Jun, 2014", "price_rate"=>10, "cost_rate"=>10, "profit"=>10} ],
  [{"x"=>"Apr, 2014", "price_rate"=>10, "cost_rate"=>10, "profit"=>10},
   {"x"=>"May, 2014", "price_rate"=>10, "cost_rate"=>10, "profit"=>10},
   {"x"=>"Jun, 2014", "price_rate"=>10, "cost_rate"=>10, "profit"=>10} ]
]

Which would leave me with

[{"x"=>"Apr, 2014", "price_rate"=>30, "cost_rate"=>30, "profit"=>30},
 {"x"=>"May, 2014", "price_rate"=>30, "cost_rate"=>30, "profit"=>30},
 {"x"=>"Jun, 2014", "price_rate"=>30, "cost_rate"=>30, "profit"=>30} ]

I've tried flattening them into a single array, merging (which never seems to give me the results I would expect), and reduce to add - but I'm getting nowhere.

Is there a concise way to do this?

EDIT Also of note is that the number of hashes in each array can vary. The example was for a quarter of a year, but the resulting solution should be agnostic enough to allow for as many or as few entries as the data set provides.

Answer 1

This is one (pure Ruby) way, which uses the form of Hash#update (aka merge! ) that uses a block to determine the values of keys present in both hashes being merged:

array.flatten.each_with_object({}) { |g,h|
  h.update(g["x"]=>g.dup) { |_,oh,nh|
    oh.update(nh) { |k,ov,nv| (k=="x") ? ov : ov+nv } } }.values
  #=> [{"x"=>"Apr, 2014", "price_rate"=>30, "cost_rate"=>30, "profit"=>30},
  #    {"x"=>"May, 2014", "price_rate"=>30, "cost_rate"=>30, "profit"=>30},
  #    {"x"=>"Jun, 2014", "price_rate"=>30, "cost_rate"=>30, "profit"=>30}]

trh pointed out that my original solution modified array , which I had missed. To avoid that, I changed g["x"]=>g to g["x"]=>g.dup .

Answer 2

Look into using deep_merge recursively. To do this with 2 hashes you would use:

hash1.deep_merge(hash2) { |key, first, last| key == 'x' ? first : first + last }

What this is doing is merging each key value, except the first column (which should always match). If you loop through all your arrays youy should be able to merge them into one using a similar strategy.

More info: http://api.rubyonrails.org/classes/Hash.html#method-i-deep_merge