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rubyruby-hash

Better way to initialize and update deeply nested Hash

I have a Hash and I want to insert some data into it at a deep level, but a key might be missing at any level. So, I am conditionally initializing it before updating its value at every level.

What would be a better way to write this or an approach that can make code less ugly?

data[:foo] ||= {}
data[:foo][:bar] ||= {}
data[:foo][:bar][:baz] ||= []
data[:foo][:bar][:baz] << 99
Solution

  • Use hash autovivification:

    data = Hash.new { |h, k| h[k] = h.dup.clear }
#⇒ {}

# or, credits to @Amadan:
data = Hash.new { |h, k| h[k] = Hash.new(&h.default_proc) }
#⇒ {}

data[:foo][:bar][:baz] = 42
data
#⇒ {:foo=>{:bar=>{:baz=>42}}}

    The trick used here is we use Hash#default_proc to create nested keys.

    For your case:

    (data[:foo][:bar][:baz] = []) << 99