Ruby - Set Value of nested hash from array of keys

Question

I learned from Access nested hash element specified by an array of keys)

that if i have a array

array = ['person', 'age']

and I have a nested hash

hash = {:person => {:age => 30, :name => 'tom'}}

I can get the value of of age by using

array.inject(hash, :fetch)

But How would I then set the value of :age to 40 with the array of keys?

August · Accepted Answer · 2015-01-29 19:33:51Z

11

You can get the hash that contains the last key in the array (by removing the last element), then set the key's value:

array.map!(&:to_sym) # make sure keys are symbols

key = array.pop
array.inject(hash, :fetch)[key] = 40

hash # => {:person=>{:age=>40, :name=>"tom"}}

If you don't want to modify the array you can use .last and [0...-1]:

keys = array.map(&:to_sym)

key = keys.last
keys[0...-1].inject(hash, :fetch)[key] = 40

edited Jan 29, 2015 at 19:33

answered Jan 28, 2015 at 23:09

August

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2 Comments

August Over a year ago

@CarySwoveland Thanks, I overlooked that. I also added an alternate solution if it's important to preserve the array.

Cary Swoveland Over a year ago

Still not testing! If you don't want to modify array, keys = array.map(&:to_sym); key = keys.last.... (Ah, yes, it's pop. I had shift on the brain.)

Cary Swoveland · Accepted Answer · 2015-01-29 08:33:13Z

0

You could use recursion:

def set_hash_value(h, array, value)
  curr_key = array.first.to_sym
  case array.size
  when 1 then h[curr_key] = value
  else set_hash_value(h[curr_key], array[1..-1], value)
  end
  h
end

set_hash_value(hash, array, 40)
  #=> {:person=>{:age=>40, :name=>"tom"}}

answered Jan 29, 2015 at 8:33

Cary Swoveland

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Comments

Marian13 · Accepted Answer · 2021-04-22 23:23:56Z

0

You can consider using the set method from the rodash gem in order to set a deeply nested value into a hash.

require 'rodash'

hash = { person: { age: 30, name: 'tom' } }

key = [:person, :age]
value = 40

Rodash.set(hash, key, value)

hash
# => {:person=>{:age=>40, :name=>"tom"}}

edited Apr 22, 2021 at 23:23

answered Apr 22, 2021 at 23:06

Marian13

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