CODEWITHSUNDEEP
ruby-on-railsrubyruby-2.1
Derek
Derek

Reputation: 12388

Array to Hash with conditional logic in Ruby?

ruby 2.1.1

Is there a way to do the logic in this piece of code in one line or a more concise manner?

user = User.new
h = Hash.new
attrs = [:name, :foo, :bar]
attrs.each do |a|
    h[a] = user[a] if user.has_attribute? a
end
return h

Upvotes: 0

Views: 320

Answers (3)

zverok
zverok

Reputation: 1400

Answers above are correct in Rails scope, I'l just add generic solution:

# assuming user[a] returns nil, if user have no a attribute
[:name, :foo, :bar].
  map{|a| [attr, user[a]]}.
  reject{|k, v| v.nil?}.
  to_h

# assuming user[a] can raise if not user.has_attribute?(a)
[:name, :foo, :bar].
   map{|a| [attr, user.has_attribute?(a) && user[a]]}.
   reject{|k, v| !v}.
   to_h

I've formatted them as NOT one-liners, but they are still one-statements :)

Basically, the trick is "invent the right method chain to convert one sequence to other", and requires to know all Enumerable sequence-transforming methods (map/select/reduce/reject/...), as well as a method to transform array of key-value pairs into hash (#to_h is standard in Ruby 2.1.1)

Upvotes: 0

Arup Rakshit
Arup Rakshit

Reputation: 118299

It seems you are on Rails. If so,then - 

attrs = [:name, :foo, :bar]
# the result hash will be returned, if last line of the method.
user.attributes.extract!(*attrs)

Look these methods extract! and attributes.

Example :

arup@linux-wzza:~/Rails/app> rails c
Loading development environment (Rails 4.1.1)
2.0.0-p451 :001 > h = { a: 1, b: 2, c: 3, d: 4 }
 => {:a=>1, :b=>2, :c=>3, :d=>4}
2.0.0-p451 :002 > h.extract!(:a ,:b ,:x)
 => {:a=>1, :b=>2}
2.0.0-p451 :003 >

Upvotes: 1

gwcoffey
gwcoffey

Reputation: 5919

If you're using Rails and User is an ActiveRecord model (which it looks like given your use of has_attribute?) then this will do the same thing:

user = User.new
...
return user.attributes.slice("name", "foo", "bar")

Or, if you really want symbols:

return user.attributes.with_indifferent_access.slice(:name, :foo, :bar)

Upvotes: 3

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