Initialising a hash of hashes

Question

Let's say I have a hash of hashes as follows:

order_history = {}

order_history[customer_id][order_id] = { :total_spend => order_spend, :date => order_date }

When I add entries into this hash I have to check whether the customer_id exists first, like so:

order_history[customer_id] = {} unless order_history.has_key?(customer_id)

Then, I can add the details for an individual order:

order_history[123][456] = { :total_spend => 200.45, :date => 2016-05-03 }

Is it possible to declare the order_history hash as a hash-of-hashes at the outset, so I don't have to do the test every time? Or is there a way of telling ruby that when a new key is created, set the value to be a new, empty hash?

score 3 · Accepted Answer · edited May 23 '17 at 11:59

3

You can try this for your hash :

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

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

For more information, this answer is from this post

edited May 23 '17 at 11:59

Community

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answered May 10 '16 at 10:28

XavM

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score 0 · Answer 2 · answered May 10 '16 at 11:03

While the answer provided by @XavM perfectly answers the question, I would drop here a reference to excellent Hashie#Mash. Using the latter, one might do for string keys:

▶ require 'hashie/mash'
▶ hm = Hashie::Mash.new
#⇒ {}
▶ hm.foo.bar
#⇒ NoMethodError: undefined method `bar' for nil:NilClass

but:

▶ hm.foo!.bar
#⇒ nil
▶ hm.foo!.bar!
#⇒ {}

Sometimes it is more handy, than defining a default_proc.

NB the correct answer to the question stated in OP is provided by @XavM, please upvote it. I just dropped it here as an addendum.

Initialising a hash of hashes

2 Answers2