Question

I want to use ordered hash.

existing_hash = { key: value1, foo: value2 }

I want add { bar: value3 } after key 'key:'
expecting_hash = { key: value1, bar: value3, foo: value2 }

My code:

existing_hash[:bar] = value3
actual_hash =  { key: value1, foo: value2, bar: value3 }

Answer 1

@Sergio is right about unordered nature of Hash, but technically it looks sorta interesting.

Could not refrain from find a solution 🙂

Here it is, though not really elegant:

# having this and need to insert 3 after 2
h = {1=>:one, 2=>:two, 4=>:four, 5=>:five}

after_key = 2
after_key_index = h.keys.index(after_key)
h1,h2 = h.partition {|k,v| h.keys.index(k) <= after_key_index }.map {|a| Hash[a]}

p h1.merge(3 => :three).merge(h2)
# => {1=>:one, 2=>:two, 3=>:three, 4=>:four, 5=>:five}

# or

h1[3] = :three
p h1.merge h2
# => {1=>:one, 2=>:two, 3=>:three, 4=>:four, 5=>:five}

And applied to your code:

h = { key: :value1, foo: :value2 }

after_key = :key
after_key_index = h.keys.index(after_key)
h1,h2 = h.partition {|k,v| h.keys.index(k) <= after_key_index }.map {|a| Hash[a]}

p h1.merge(:bar => :value3).merge(h2)
# => {:key=>:value1, :bar=>:value3, :foo=>:value2}

# or

h1[:bar] = :value3
p h1.merge h2
# => {:key=>:value1, :bar=>:value3, :foo=>:value2}