Merging keys and values from hash in Ruby - ruby

Question

I have a hash with the number of occurrences of cities from a model and I want to merge nil or blank keys and values into one and rename the new single key
for example
#raw_data = {nil => 2, "" => 2, "Berlin" => 1, "Paris" => 1}
# to
#corrected_data = {"undefined" => 4, "Berlin" => 1, "Paris" => 1}
I have looked into the merge method from the Rubydoc but it only merges if two keys are similar, but in this case nil and "" are not the same.
I could also create a new hash and add if nil or blank statements and add the values to a new undefined key, but it seems tedious.

Answer 1

I'd do :
#raw_data = {nil => 2, "" => 2, "Berlin" => 1, "Paris" => 1}
key_to_merge = [nil, ""]
#correct_data = #raw_data.each_with_object(Hash.new(0)) do |(k,v), out_hash|
next out_hash['undefined'] += v if key_to_merge.include? k
out_hash[k] = v
end
#correct_data # => {"undefined"=>4, "Berlin"=>1, "Paris"=>1}

Answer 2

Ruby cannot automatically determine what do you want to do with values represented by two "similar" keys. You have to define the mapping yourself. One approach would be:
def undefined?(key)
# write your definition of undefined here
key.nil? || key.length == 0
end
def merge_value(existing_value, new_value)
return new_value if existing_value.nil?
# your example seemed to add values
existing_value + new_value
end
def corrected_key(key)
return "undefined" if undefined?(key)
key
end
#raw_data = {nil => 2, "" => 2, "Berlin" => 1, "Paris" => 1}
#raw_data.reduce({}) do |acc, h|
k, v = h
acc[corrected_key(k)] = merge_value(acc[corrected_key(k)], v)
acc
end
# {"undefined" => 4, "Berlin" => 1, "Paris" => 1}