Does ruby have similiar multidimensional array like in php?

Question

like in php:

$input = [
      'a' => 'A',
      'b' => 'B',
      'cdef' => [
             'c' => 'C',
             'd' => 'D',
             'ef' => [
                  'e' => 'E',
                  'f' => 'F'
             ]
      ]
]

maybe use Hash? never used ruby before :)

When I worte code:

input = Hash.new
input['a'] = 'A'
input['b'] = 'B'
input['cdef']['c'] = 'C'
input['cdef']['d'] = 'D'
input['cdef']['ef']['e'] = 'E'
input['cdef']['ef']['f'] = 'F'

error at

  input['cdef']['c'] = 'C'

message :

[]=' for nil:NilClass

input = { 'a' => 'A', 'b' => 'B', 'cdef' => { 'c' => 'C', ... } }. — mu is too short
– mu is too short, Commented Sep 21, 2016 at 2:56

Aleksei Matiushkin · Accepted Answer · 2016-09-21 05:56:28Z

3

Although the answer by @davidhu2000 is more or less correct, I would go with more robust solution: using default_proc in the constructor. The dup.clear magic is to recursively pass the default_proc through to deeply nested elements:

input = Hash.new { |h, k| h[k] = h.dup.clear }
input['a'] = 'A' 
input['b'] = 'B' 
input['cdef']['c'] = 'C' 
input['cdef']['d'] = 'D' 
input['cdef']['ef']['e'] = 'E' 
input['cdef']['ef']['f'] = 'F' 

input

That way one does not need ugly redundant assignments:

input['cdef'] = {}
input['cdef']['ef'] = {}

Ninja assignment:

input = Hash.new { |h, k| h[k] = h.dup.clear }
input['a1']['a2']['a3']['a4']['a5'] = 42
input
#⇒ {"a1" => {"a2" => {"a3" => {"a4" => {"a5" => 42}}}}}

answered Sep 21, 2016 at 5:56

Aleksei Matiushkin

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5 Comments

Aleksei Matiushkin Over a year ago

@SergioTulentsev thanks. It costs producing temporary redundant copy of the initial (and all nested having children) hash, though. But on human-operated hashes it should work fine.

Allen Jz Over a year ago

@mudasobwa thx!... but how do I use this trick after I copy a clone of another multidimentional hash into input,like I have origin = {'a'=>1,'b'=>2,'cd'=>{'c'=>3,'d'=>4}}, and I copy origin into input,using input = origin.clone, then ur thick doesn't work,maybe clone operation has ruin the structure of input?

Aleksei Matiushkin Over a year ago

In the first place, please stop calling hashes “multidimentional arrays,” since they are not arrays by any means and php just implied a wrong usage of this term. Secondary, I did not understand the problem. As origin hash has default_proc declared, it’s clone has is either. The last, but not least: you should’ve asked another question on that, whether you have one.

Allen Jz Over a year ago

f, I called it "multidimentional hash",since u haven't go through my question carefully with respect, I'm ok with it , s, thx, I know where the point is, lbnl, my question has not been solved, why can't I ask more, MDZZ

Aleksei Matiushkin Over a year ago

Indeed, there was a “multidimentional hash," nevertheless, it’s a plain old good “hash.” Please also use English, since there is not a chatroom for 14-yo cheerleaders. Your problem has been solved, now you have another one about cloning hashes—go ask it. SO is tended to implement a model 1 question per posting to make it easier for future readers to narrow their problem amongst the variety of already existing answers.

davidhu · Accepted Answer · 2016-09-21 03:00:30Z

1

To fix your error, you need to initialize an empty hash before assigning a key-value pair.

input = Hash.new
input['a'] = 'A'               #=> {"a"=>"A"}
input['b'] = 'B'               #=> {"a"=>"A", "b"=>"B"}
input['cdef'] = {}             #=> {"a"=>"A", "b"=>"B", "cdef"=>{}}
input['cdef']['c'] = 'C'       #=> {"a"=>"A", "b"=>"B", "cdef"=>{"c"=>"C"}}
input['cdef']['d'] = 'D'       #=> {"a"=>"A", "b"=>"B", "cdef"=>{"c"=>"C", "d"=>"D"}}
input['cdef']['ef'] = {}       #=> {"a"=>"A", "b"=>"B", "cdef"=>{"c"=>"C", "d"=>"D", "ef"=>{}}}
input['cdef']['ef']['e'] = 'E' #=> {"a"=>"A", "b"=>"B", "cdef"=>{"c"=>"C", "d"=>"D", "ef"=>{"e"=>"E"}}}
input['cdef']['ef']['f'] = 'F' #=> {"a"=>"A", "b"=>"B", "cdef"=>{"c"=>"C", "d"=>"D", "ef"=>{"e"=>"E", "f"=>"F"}}}

answered Sep 21, 2016 at 3:00

davidhu

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2 Comments

Aleksei Matiushkin Over a year ago

I wonder how will assignment of nested element on level 10 look like with this approach. Please check my answer.

davidhu Over a year ago

it'll be ugly, i definitely like your solution better.

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