Understanding Ruby Code

Question

I need some help understanding the below ruby code.

counted = Hash.new(0)
parsed_reponse["result"]["data"].each { |h| counted[h["version"]] += 1 }
counted = Hash[counted.map {|k,v| [k,v.to_s] }]

I understand line 1 creats a hash which I believe is similar to a dictionary in python.
Line 2 loops through my json data set a adds a new key and value pair if none exits and increments the count if 1 does exist.
What does the 3rd line do?

Hash[ [ [key, value], ... ] ] → new_hash -- Creates a new hash populated with the given objects. — axiac
– axiac, Commented Nov 5, 2017 at 10:45

Ilya · Accepted Answer · 2017-11-05 11:48:49Z

1

Your last line just converts all values to String:

Hash[{a: 2, b: 3}.map {|k, v| [k, v.to_s]}]
#=> {:a=>"2", :b=>"3"}

I would refactor it to:

counted.transform_values!(&:to_s) # for ruby >= 2.4
#=> {:a=>"1", :b=>"2"}

Or for older versions:

counted.each { |k, v| counted[k] = v.to_s }

Because:

Both steps are redundant, you can just modify existing hash.

answered Nov 5, 2017 at 10:38

Ilya

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2 Comments

Is there documentation for .map. method. I tried looking here, ruby-doc.org/core-2.3.1/Hash.html, but found nothing.

In recent Ruby versions you could write counted.transform_values!(&:to_s)