How do you access nested elements of a hash with a single string key?

Question

I'm fooling around with Ruby and basically I have

@trans = { :links => {
    :quick_notes => "aaaaaaa"
  }
}

I want to call something like

def t
  #...something
end
t('links.quick_notes')

to access

trans[:links][:quick_notes]

I'm basically trying to achieve the same functionality like when using Internationalizations

I18n.t('something.other.foo')

sofar I came up with this approach

 def t(key)
   a=''
   key.to_s.split('.').each{|key|  a+="[:#{key}]" } 
   #now a == "[:links][:quick_notes]"
   #but I cant figure out how can I call it on  @trans variable

 end

 t('links.quick_notes')

Any ideas ? thanx

This is a fun exercise in recursion. – Jul 12 '11 at 22:36 — , Jul 12 '11 at 22:36

score 13 · Accepted Answer · answered Jul 12 '11 at 22:41

13

You can get there with inject:

def t(key)
    key.to_s.split('.').inject(@trans) { |h, k| h[k.to_sym] }
end

Error checking and "no such entry" checking is left as an exercise.

answered Jul 12 '11 at 22:41

mu is too short

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5

Even cuter: `key.to_s.split('.').map(&:to_sym).inject(@trans, :[])` – Marc-André Lafortune Jul 12 '11 at 23:27
@Marc-André: That is an interesting take on it. My block version draws my eyes to the important bit and makes it easy to "grok at a glance" for me though. Mostly a matter of preference and what you're used to though. – mu is too short Jul 12 '11 at 23:44
@mu & @pst: It's cute, but I completely agree it's not completely intuitive :-) – Marc-André Lafortune Jul 13 '11 at 03:42
Correct me if I'm wrong... For @Marc-AndréLafortune's solution works in general, we have to assure that hash is `HashWithIndifferentAccess` – Andre Figueiredo May 21 '15 at 17:58
@AndreFigueiredo We're both assuming that the hash has symbol keys. – mu is too short May 21 '15 at 18:12
We're not assuming, that's clear from the question. Notice the call to `to_sym`. – Marc-André Lafortune May 22 '15 at 10:14
@Marc-AndréLafortune: Yes the question implicitly states that the keys are symbols, our solutions are also assuming that the keys are symbols. – mu is too short May 22 '15 at 21:27

score 1 · Answer 2 · edited Jan 07 '16 at 21:30

1

If you are looking for something that interpolates %{variable}, including Array support, I've been using this:

def interpolate(string, hash)
  string.gsub(/%\{([^\}]*)\}/).each { |match| match[/^%{(.*)}$/, 1].split('.').inject(hash) { |h, k| h[(k.to_s == k.to_i.to_s) ? k.to_i : k.to_sym] } }
end

edited Jan 07 '16 at 21:30

Nathaniel Ford

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answered Jan 07 '16 at 21:03

Matteo Cerutti

11
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steenslag · Answer 3 · 2016-01-07T21:37:38.837

1

Since Ruby 2.3 Hash has a dig method. "no such entry" checking is built in: if any of the keys is missing, then the whole expression returns nil. Usage:

@trans = { :links => {
    :quick_notes => "aaaaaaa"
  }
}

def t (str)
  syms = str.split(".").map(&:to_sym)
  @trans.dig(*syms)
end
p t('links.quick_notes')  # => "aaaaaaa"

edited Jan 07 '16 at 21:37

answered Jan 07 '16 at 21:18

steenslag

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score 1 · Answer 4 · 2011-07-12T23:08:43.427

For what it's worth, here is some manky code that shows the use of recursion.

def getKeyChain (obj, parts)
  if !obj || parts.size == 0
    # this is the base case
    obj
  else
    # this is the recursive case
    key = parts[0]
    if key.match(/^:/)
      key = key[1..key.size].to_sym
    end
    # each time recursing, pass a new state.
    # in this case, the value for the "key" and the remaining parts
    # that need resolving
    getKeyChain(obj[key], parts[1..parts.size])
  end
end

def getCompoundKey (obj, compound)
  # helper makes it easier to call while not making the
  # recursive function more complex.
  getKeyChain(obj, compound.split("."))
end

h0 = {:x => "hello"}
h1 = {"a" => {:b => "world"}}
puts getCompoundKey(h0, ":x")   # => hello
puts getCompoundKey(h1, "a.:b") # => world

Many improvements can be made... "use at own peril".

Happy coding.

score 0 · Answer 5 · answered Mar 06 '13 at 06:19

Another addition - If you have json or a hash that includes arrays as well as hashes - maybe something like this:

@trans = { :links => [ {
    :quick_notes => "aaaaaaa"
  },
  {
    :quick_notes => "bbbbbbb"
  } ],
  :page => 1
}

You can include a test of position in an array, you can do this sort of thing.

def t(key)
  key.split('.').inject(@trans) { |h,v| h.send('[]',v.to_i.to_s.eql?(v) ? v.to_i : v) }
end

This would allow you to pass a key like this

t('links.1.quick_notes')

and get the answer 'bbbbbb'

How do you access nested elements of a hash with a single string key?

5 Answers5

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