Access Ruby Hash Using Dotted Path Key String

Access Ruby Hash Using Dotted Path Key String

Just split on a dot in the path and iterate over this to find the right hash?

path.split(".").inject(hash) { |hash, key| hash[key] }

Alternatively you can build a new hash by iterating recursively over the whole structure:

def convert_hash(hash, path = "")
  hash.each_with_object({}) do |(k, v), ret|
    key = path + k

    if v.is_a? Hash
      ret.merge! convert_hash(v, key + ".")
    else
      ret[key] = v
    end
  end
end

Ruby dot notation to nested hash keys

Try this

f = "root/sub-1/sub-2/file"   
f.split("/").reverse.inject{|a,n| {n=>a}} #=>{"root"=>{"sub-1"=>{"sub-2"=>"file"}}}

Use an Array to access nested Hash keys

You could make use of the newer method Hash#dig (ruby 2.3+) to access the nested hash, and then set the value on that:

# ideally this might be a method on Hash, so you wouldn't need to pass it in
def deep_set(hash, path, value)
  *path, final_key = path
  to_set = path.empty? ? hash : hash.dig(*path)

  return unless to_set
  to_set[final_key] = value
end

hash = {
  "foo" => {
    "bar" => { }
  }
}

deep_set(hash, ["foo", "bar", "baz"], "xxxxxx")
deep_set(hash, ["baz"], "yyyyyy")
deep_set(hash, ["foo", "baz", "bar"], "zzzzzz")
puts hash
# => {"foo"=>{"bar"=>{"baz"=>"xxxxxx"}}, "baz"=>"yyyyyy"}

How to transform dot-notation string keys in a Hash into a nested Hash?

This code may need to be refactored but it works for the input you have given.

hash = { 
  :axis => [1,2], 
  "coord.x" => [12,13], 
  "coord.y" => [14,15], 
}

new_hash = {}
hash.each do |key, val|
  new_key, new_sub_key = key.to_s.split('.')
  new_key = new_key.to_sym
  unless new_sub_key.nil?
    new_sub_key = new_sub_key.to_sym
    new_hash[new_key] = {} if new_hash[new_key].nil?
    new_hash[new_key].merge!({new_sub_key => val})
  else
    new_hash.store(key, val)
  end
end

new_hash # => {:axis=>[1, 2], :coord=>{:x=>[12, 13], :y=>[14, 15]}}

Accessing elements of nested hashes in ruby

The way I usually do this these days is:

h = Hash.new { |h,k| h[k] = {} }

This will give you a hash that creates a new hash as the entry for a missing key, but returns nil for the second level of key:

h['foo'] -> {}
h['foo']['bar'] -> nil

You can nest this to add multiple layers that can be addressed this way:

h = Hash.new { |h, k| h[k] = Hash.new { |hh, kk| hh[kk] = {} } }

h['bar'] -> {}
h['tar']['zar'] -> {}
h['scar']['far']['mar'] -> nil

You can also chain indefinitely by using the default_proc method:

h = Hash.new { |h, k| h[k] = Hash.new(&h.default_proc) }

h['bar'] -> {}
h['tar']['star']['par'] -> {}

The above code creates a hash whose default proc creates a new Hash with the same default proc. So, a hash created as a default value when a lookup for an unseen key occurs will have the same default behavior.

EDIT: More details

Ruby hashes allow you to control how default values are created when a lookup occurs for a new key. When specified, this behavior is encapsulated as a Proc object and is reachable via the default_proc and default_proc= methods. The default proc can also be specified by passing a block to Hash.new.

Let's break this code down a little. This is not idiomatic ruby, but it's easier to break it out into multiple lines:

1. recursive_hash = Hash.new do |h, k|
2.   h[k] = Hash.new(&h.default_proc)
3. end

Line 1 declares a variable recursive_hash to be a new Hash and begins a block to be recursive_hash's default_proc. The block is passed two objects: h, which is the Hash instance the key lookup is being performed on, and k, the key being looked up.

Line 2 sets the default value in the hash to a new Hash instance. The default behavior for this hash is supplied by passing a Proc created from the default_proc of the hash the lookup is occurring in; ie, the default proc the block itself is defining.

Here's an example from an IRB session:

irb(main):011:0> recursive_hash = Hash.new do |h,k|
irb(main):012:1* h[k] = Hash.new(&h.default_proc)
irb(main):013:1> end
=> {}
irb(main):014:0> recursive_hash[:foo]
=> {}
irb(main):015:0> recursive_hash
=> {:foo=>{}}

When the hash at recursive_hash[:foo] was created, its default_proc was supplied by recursive_hash's default_proc. This has two effects:

1. The default behavior for recursive_hash[:foo] is the same as recursive_hash.
2. The default behavior for hashes created by recursive_hash[:foo]'s default_proc will be the same as recursive_hash.

So, continuing in IRB, we get the following:

irb(main):016:0> recursive_hash[:foo][:bar]
=> {}
irb(main):017:0> recursive_hash
=> {:foo=>{:bar=>{}}}
irb(main):018:0> recursive_hash[:foo][:bar][:zap]
=> {}
irb(main):019:0> recursive_hash
=> {:foo=>{:bar=>{:zap=>{}}}}

Find key/value pairs deep inside a hash containing an arbitrary number of nested hashes and arrays

Here's a simple recursive solution:

def nested_hash_value(obj,key)
  if obj.respond_to?(:key?) && obj.key?(key)
    obj[key]
  elsif obj.respond_to?(:each)
    r = nil
    obj.find{ |*a| r=nested_hash_value(a.last,key) }
    r
  end
end

h = { foo:[1,2,[3,4],{a:{bar:42}}] }
p nested_hash_value(h,:bar)
#=> 42

Unable to use dot syntax for ruby hash

Hash does not have dot-syntax for it's keys. OpenStruct does:

require 'ostruct'
hash = {:name => 'John'}
os = OpenStruct.new(hash)
p os.name #=> "John"

NOTE: Does not work with nested hashes.

Build paths of edge keys in nested hashes in ruby

def recurse(h)
  h.flat_map do |k,v|
    if v.is_a?(Hash)      
      recurse(v).map { |str| "%s.%s" % [k.to_s, str] }
    else
      k.to_s
    end
  end
end

h = {a: {m: {b: 2, c:1}, d: {e: {f: nil}, g: 3}}}
recurse(h)
  #=> ["a.m.b", "a.m.c", "a.d.e.f", "a.d.g"] 

h = {a: {m: {b: 2, c:1}, d: 5 }, e: {f: {g: nil}, h: 3}}
recurse(h)
  #=> ["a.m.b", "a.m.c", "a.d", "e.f.g", "e.h"]

hash['key'] to hash.key in Ruby

>> require 'ostruct'
=> []
>> foo = {'bar'=>'baz'}
=> {"bar"=>"baz"}
>> foo_obj = OpenStruct.new foo
=> #<OpenStruct bar="baz">
>> foo_obj.bar
=> "baz"
>>

Classic hash to dot-notation hash

Here's the cleanest solution I could come up with right now:

def dot_it(object, prefix = nil)
  if object.is_a? Hash
    object.map do |key, value|
      if prefix
        dot_it value, "#{prefix}.#{key}"
      else
        dot_it value, "#{key}"
      end
    end.reduce(&:merge)
  else
    {prefix => object}
  end
end

Test:

input = {a: {b: {"1" => 1, "2" => 2}, d: "Something"}, b: {c: 1}}

p dot_it input

Output:

{"a.b.1"=>1, "a.b.2"=>2, "a.d"=>"Something", "b.c"=>1}

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