Recursively set hash keys from an array of keys
I need a function that can take an array of type [:a, :b, :c]
and set the hash keys recursively, creating what it needs when it goes.
hash = {}
hash_setter(hash, [:a, :b, :c], 'value')
hash #=> {:a => {:b => {:c => 'value' } } }
hash_setter(hash, [:a, :b, :h], 'value2')
hash #=> {:a => {:b => {:c => 'value', :h => 'value2' } } }
I know Ruby 2.3 dig
can be used to get this way, although it doesn't give you an answer. If there was an equivalent to a setter that would be what I'm looking for.
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code
def nested_hash(keys, v, h={})
return subhash(keys, v) if h.empty?
return h.merge(subhash(keys, v)) if keys.size == 1
keys[0..-2].reduce(h) { |g,k| g[k] }.update(keys[-1]=>v)
h
end
def subhash(keys, v)
*first_keys, last_key = keys
h = { last_key=>v }
return h if first_keys.empty?
first_keys.reverse_each.reduce(h) { |g,k| g = { k=>g } }
end
<strong> Examples
h = nested_hash([:a, :b, :c], 14) #=> {:a=>{:b=>{:c=>14}}}
i = nested_hash([:a, :b, :d], 25, h) #=> {:a=>{:b=>{:c=>14, :d=>25}}}
j = nested_hash([:a, :b, :d], 99, i) #=> {:a=>{:b=>{:c=>14, :d=>99}}}
k = nested_hash([:a, :e], 104, j) #=> {:a=>{:b=>{:c=>14, :d=>99}, :e=>104}}
nested_hash([:f], 222, k) #=> {:a=>{:b=>{:c=>14, :d=>99}, :e=>104}, :f=>222}
Note that the value is :d
overridden when calculated j
. Also note that:
subhash([:a, :b, :c], 12)
#=> {:a=>{:b=>{:c=>12}}}
This mutates the hash h
. If this is not desired, you can insert the line
f = Marshal.load(Marshal.dump(h))
after the line return subhash(keys, v) if h.empty?
and change subsequent references h
to f
. Methods from the Marshal module can be used to create a deep copy of the hash, so the original hash will not be mutated.
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def set_value_for_keypath(initial, keypath, value)
temp = initial
for key in keypath.first(keypath.count - 1)
temp = (temp[key] ||= {})
end
temp[keypath.last] = value
return initial
end
initial = {:a => {:b => {:c => 'value' } } }
set_value_for_keypath(initial, [:a, :b, :h], 'value2')
initial
Or, if you prefer something a little more unreadable:
def set_value_for_keypath(initial, keypath, value)
keypath.first(keypath.count - 1).reduce(initial) { |hash, key| hash[key] ||= {} }[keypath.last] = value
end
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