Hash1 = {
map1: {city: 'Berlin', country: 'Germany'},
map2: {city: 'Toronto', country: 'Canada'},
map3: {city: 'Boston', country: 'USA' }
}
Okay so I want to build a hash that looks as follows:
newHash = {
Berlin: 'map1',
Toronto: 'map2',
Boston: 'map3'
}
How do I loop through Hash1 and build newHash.
Hash1.each_with_object({}) do |(key, value), acc|
# what do I do inside this loop?
end
Hash1.map { |k, v| [v[:city].to_sym, k.to_s] }.to_h
#⇒ {:Berlin=>"map1", :Toronto=>"map2", :Boston=>"map3"}
data = {
map1: {city: 'Berlin', country: 'Germany'},
map2: {city: 'Toronto', country: 'Canada'},
map3: {city: 'Boston', country: 'USA' }
}
new_data = data.reduce({}) { |h, (k, v)| h[v[:city].to_sym] = k.to_s; h }
puts new_data #=> {:Berlin=>"map1", :Toronto=>"map2", :Boston=>"map3"}
each_with_object here. Besides ugly ; h, reduce recreates the object on each iteration.
reduce doesn't recreate the object. It passes the object which is returned by the block into the next iteration. So if the block returns the same object (like h above), no additional objects will be created. (nonetheless, each_with_object would be the better tool)output = {}
hash.each do |key, value|
output[:"#{value[:city]}"] = key.to_s
end
puts output
# {:Berlin=>"map1", :Toronto=>"map2", :Boston=>"map3"}
For the exact output style, you have to use the Ruby 1.9 or higher version.
each with preliminary created local variable. Use each_with_object instead.I'm showing just one of many methods below
new_hash = Hash.new
Hash1.each do |key, value|
new_hash[value[:city]] = key
end
each with preliminary created local variable instead of map/reduce. Also, value['city'] would be nil.each, a bad idea here?each is for enumerating. reduce/each_with_object is for reducing. The code is semantically incorrect.