Sorting an hash given another hash including infor

问题:

I am using Ruby on Rails 3.0.7 and I would like to sort an hash considering a preset order by returning a sorted array or even a new sorted hash. That is, given the following hash, say HASH1 (for which I consider its values to indicate the order method from 1 to 4)

{
  :dog  => 3,
  :cat  => 2,
  :pig  => 4,
  :frog => 1
}

I would like to sort this other hash by key, say HASH2, by considering the order given in HASH1 values

{
  :cat  => 'cat_value',
  :dog  => 'dog_value',
  :frog => 'frog_value',
  :pig  => 'pig_value'
}

So, in the above case, I should have the outputted\ordered hash like the following:

{
  :frog => 'frog_value', # Order indicated by ':frog => 1' in the HASH1
  :cat  => 'cat_value',  # Order indicated by ':cat => 2'  in the HASH1
  :dog  => 'dog_value',  # Order indicated by ':dog => 3'  in the HASH1
  :pig  => 'pig_value'   # Order indicated by ':pig => 4'  in the HASH1
}

or

[
  ["frog", 'frog_value'], # Order indicated by ':frog => 1' in the HASH1
  ["cat", 'cat_value'],   # Order indicated by ':cat => 2'  in the HASH1
  ["dog", 'dog_value'],   # Order indicated by ':dog => 3'  in the HASH1
  ["pig", 'pig_value']    # Order indicated by ':pig => 4'  in the HASH1
]

How can I do that?

回答1:

Use Hash#sort_by:

hash = {
  :cat  => [2],
  :frog => [1],
  :pig  => [4],
  :dog  => [3]
}

order = {
  :dog  => 3,
  :cat  => 2,
  :pig  => 4,
  :frog => 1
}

# array of k, v pairs
p sorted_array = hash.sort_by {|k, v| order[k]}
p sorted_hash = Hash[sorted_array]

Output

[[:frog, [1]], [:cat, [2]], [:dog, [3]], [:pig, [4]]]
{:frog=>[1], :cat=>[2], :dog=>[3], :pig=>[4]}