How to replace all hash keys having a '.'?

Question

I am using Ruby on Rails 4 and I would like to replace all hash keys so to change the hash from

h_before = {:"aaa.bbb" => 1, :c => 2, ...}

to

h_after = {:bbb => 1, :c => 2, ...}

That is, I would like to someway "demodulize" all hash keys having the .. How can I make that?

Answer 1

Since there are a bunch of answers claiming to do the same thing, I thought it was time to post some benchmarks:

require 'fruity'

h_before = {:"aaa.bbb" => 1, :c => 2}

def cdub_test(hash)
  Hash[hash.map {|k, v| [k.to_s.gsub(/^.*\./,"").to_sym, v]}]
end

def matt_test(old_hash)
  Hash[old_hash.map { |k,v| [ k.to_s.sub(/.*\./,'').to_sym, v ] }]
end

class Hash
  require 'active_support/core_ext/hash/indifferent_access'
  def grep_keys(pattern)
    return inject(HashWithIndifferentAccess.new){|h, (k, v)|
      h[$1 || k] = v  if pattern =~ k.to_s ;  h }
  end
end

def phlip_test(hash)
  hash.grep_keys(/\.(\w+)$/)
end

def bjhaid_test(hash)
  hash.each_with_object({}){|(k, v),h| h[k.to_s.split(".").last.to_sym] = v}
end

def sawa_test(hash)
  hash.inject({}){|h, (k, v)| h[k.to_s.split(".").last.to_sym] = v; h}
end

compare do
    cdub   { cdub_test(h_before)   }
    matt   { matt_test(h_before)   }
    phlip  { phlip_test(h_before)  }
    bjhaid { bjhaid_test(h_before) }
    sawa   { sawa_test(h_before)   }
end

Which outputs:

Running each test 1024 times. Test will take about 1 second.
bjhaid is similar to sawa
sawa is faster than matt by 60.00000000000001% ± 10.0%
matt is faster than phlip by 30.000000000000004% ± 10.0% (results differ: {:bbb=>1, :c=>2} vs {"bbb"=>1})
phlip is similar to cdub (results differ: {"bbb"=>1} vs {:bbb=>1, :c=>2})

Notice that phlip's code doesn't return the desired results.

Answer 2

each_with_object is a cleaner and shorter approach than inject from the answer:

h_before.each_with_object({}){|(k, v),h| h[k.to_s.split(".").last.to_sym] = v}
=> {:bbb=>1, :c=>2}

Answer 3

My grep_keys has never failed me here:

class Hash
  def grep_keys(pattern)
    return inject(HashWithIndifferentAccess.new){|h, (k, v)| 
      h[$1 || k] = v  if pattern =~ k.to_s ;  h }
  end
end

It returns a shallow-copy of the Hash, but only with the matched keys. If the input regular expression contains a () match, the method replaces the key with the matched value. (Note this might merge two or more keys, and discard all but a random value for them!) I use it all the time to cut up a Rails param into sub-params containing only the keys that some module needs.

{:"aaa.bbb" => 1, :c => 2 }.grep_keys(/\.(\w+)$/) returns {"bbb"=>1}.

This method upgrades your actual problem to "how to define a regexp that matches what you mean by 'having a ".".'"

Answer 4

1.9.3p448 :001 > hash = {:"aaa.bbb" => 1, :c => 2 }
 => {:"aaa.bbb"=>1, :c=>2} 

1.9.3p448 :002 > Hash[hash.map {|k, v| [k.to_s.gsub(/^.*\./,"").to_sym, v]}]
 => {:bbb=>1, :c=>2} 

Answer 5

h_before = {:"aaa.bbb" => 1, :c => 2}
h_after =
h_before.inject({}){|h, (k, v)| h[k.to_s.split(".").last.to_sym] = v; h}
# => {:bbb = > 1, :c => 2}

Answer 6

old_hash = {:"aaa.bbb" => 1, :c => 2 }
new_hash = Hash[old_hash.map { |k,v| [ k.to_s.sub(/.*\./,'').to_sym, v ] }]