How to get value of key or key presence from nested hash?

Question

How do I get the value of a key or the key's presence from a nested hash?

For example:

a = { "a"=> { "b" => 1, "c" => { "d" => 2, "e" => { "f" => 3 } }}, "g" => 4}

Is there any direct method to get the value of "f"? Or is there a method to know the presence of key in the nested hash?

Possible duplicate of Ruby Style: How to check whether a nested hash element exists — Ryenski
– Ryenski, Commented May 25, 2016 at 18:54

sawa · Accepted Answer · 2013-06-05 12:33:01Z

5

%w[a c e f].inject(a, &:fetch) # => 3
%w[a c e x].inject(a, &:fetch) # > Error key not found: "x"
%w[x].inject(a, &:fetch) # => Error key not found: "x"

Or, to avoid errors:

%w[a c e f].inject(a, &:fetch) rescue "Key not found" # => 3
%w[a c e x].inject(a, &:fetch) rescue "Key not found"  # => Key not found
%w[x].inject(a, &:fetch) rescue "Key not found"  # => Key not found

answered Jun 5, 2013 at 12:33

sawa

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user946611 · Accepted Answer · 2013-06-05 12:55:47Z

2

def is_key_present?(hash, key)
  return true if hash.has_key?(key)
  hash.each do |k, v|
    return true if v.kind_of?(Hash) and is_key_present?(v, key)
  end
  false
end

> is_key_present?(a, 'f')
=> true

answered Jun 5, 2013 at 12:55

user946611

Comments

Alissa H · Accepted Answer · 2022-08-01 23:24:04Z

0

A slightly different version of the answer provided by sawa:

%w[a c e f].inject(a) { |a, key| a.fetch(key, {}) }

The difference is that an empty hash will be returned if a key is not found at any point in the hierarchy, rather than an exception being raised. It is probably better to raise an exception in most cases, but this is an alternative depending on your use case.

answered Aug 1, 2022 at 23:24

Alissa H

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