I have an object that has attributes name and data, among others. I want to create a hash that uses the name as the key and the data (which is an array) as the value. I can't figure out how to reduce the code below using map. Is it possible?
def fc_hash
fcs = Hash.new
self.forecasts.each do |fc|
fcs[fc.name] = fc.data
end
fcs
end
Use Hash[]:
Forecast = Struct.new(:name, :data)
forecasts = [Forecast.new('bob', 1), Forecast.new('mary', 2)]
Hash[forecasts.map{|forecast| [forecast.name, forecast.data]}]
# => {"mary"=>2, "bob"=>1}
def fc_hash
forecasts.each_with_object({}) do |forecast, hash|
hash[forecast.name] = forecast.data
end
end
I always use inject or reduce for this:
self.forecasts.reduce({}) do |h,e|
h.merge(e.name => e.data)
end
Hash[*self.forecases.map{ [fc.name, fc.data]}.flatten]
Hash[] is but also what * does in that context. It's clever and concise, but a bit too intense for one line.
flatten, they're just noise as Hash[] is quite happy with an array-of-arrays. You're also missing something in the map block.With Ruby 2.1 and onward, you could also use Array#to_h
self.forecasts.to_h { |forecast| [forecast.name, forecast.data] }
mapreturns an array, and will not return a hash. But that said, there isn't really anything wrong with this code. Why not use it just like you have it?forecasts? Particularly, what is its class?Forecastinstances, doesn't it?{ }is almost always preferable toHash.new. The only reason to call the formal constructor is for passing in defaults, likeHash.new(0)orHash.new { |h,k| ... }.