One liner nested hash creation in ruby? (I come from perl)

Question

I am a perl person and I have made hashes like this for awhile:

my %date;

#Assume the scalars are called with 'my' earlier

$date{$month}{$day}{$hours}{$min}{$sec}++

Now I am learning ruby and I have so far found that using this tree is the way to do many keys and a value. Is there any way to use the simple format that I use with perl using one line?

 @date = {                                                                                                                                                                      
        month => {                                                                                                                                                                 
          day => {                                                                                                                                                                 
           hours => {                                                                                                                                                              
              min => {                                                                                                                                                             
                sec => 1                                                                                                                                                           
              }                                                                                                                                                                    
            }                                                                                                                                                                      
          }                                                                                                                                                                        
        }                                                                                                                                                                          

      }                   

Answer 1

Using symbols seemed to work:

ree-1.8.7-2009.10 > @date = {:month =>{:day => {:hours => {:min => {:sec => 1 } } } } }
 => {:month=>{:day=>{:hours=>{:min=>{:sec=>1}}}}} 

I can then retrieve the val like this:

ree-1.8.7-2009.10 > @date[:month][:day]
 => {:hours=>{:min=>{:sec=>1}}}

Answer 2

It doesn't look like Ruby can do autovivification from the start, but you can easily add in that functionality. A search for "ruby autovivification" on Google gives:

http://t-a-w.blogspot.com/2006/07/autovivification-in-ruby.html

Which contains a decent example of how to create a hash that will work the way you are looking for.

http://stackoverflow.com/questions/1503671/ruby-hash-autovivification-facets might also be helpful.

Answer 3

Unfortunately, there is no simple, practical way. A Ruby equivalent would be an ugly, ugly beast like:

((((@date[month] ||= {})[day] ||= {})[hours] ||= {})[min] ||= {})[sec] = 1

There is a way to assign default values for missing keys in hashes, though:

@date = Hash.new { |hash, key| hash[key] = {} }

# @date[:month] is set to a new, empty hash because the key is missing.
@date[:month][:day] = 1

Unfortunately this does not work recursively.

...unless you create it yourself; hooray for Ruby!

class Hash
  def self.recursive
    new { |hash, key| hash[key] = recursive }
  end
end

@date = Hash.recursive
@date[month][day][hours][min][sec] = 1
# @date now equals {month=>{day=>{hours=>{min=>{sec=>1}}}}}

Keep in mind, though, that all unset values are now {} rather than nil.

Answer 4

You can use the Facets gem's Hash.autonew to do the same thing as the recursive function given in Molf's answer.