Want to pick a certain set of key/value pairs from a Ruby hash? You might do this:
hash = {:foo => "bar", :bar => "baz", :baz => "boo"}
hash.select { |k,v| [:foo, :bar].include?(k) }
# returns [[:foo, "bar"], [:bar, "baz"]]
Kind of messy. We can do better by reopening the Hash class this way:
class Hash
def pick(*values)
select { |k,v| values.include?(k) }
end
end
Now our selection works like this:
hash = {:foo => "bar", :bar => "baz", :baz => "boo"}
hash.pick(:foo, :bar)
# returns [[:foo, "bar"], [:bar, "baz"]]
Ruby is a wonderful language. This is one small example of how having access to existing classes can be incredibly powerful. With this power comes great responsibility. Wield your power wisely.
If you’re using Rails, then ActiveSupport::CoreExtensions::Hash::Slice provides a slice() method to slice a hash, and this is automatically added to the Hash class for you. Its usage is exactly as given above, except that it returns a hash instead of an array of pairs.
You can use facets Hash method slice.
h.slice(:foo,:bar) #=> another hash
h.slice(:foo,:bar).to_a #=> to convert the hash into array.
http://facets.rubyforge.org/doc/index.html
How about:
class Hash
def pick(*values)
pairs = select { |k,v| values.include?(k) }
Hash[*pairs.flatten]
end
end
hash.pick(:foo, :bar)
#returns {:bar=>"baz", :foo=>"bar"}