Set multiple keys to the same value at once for a Ruby hash

Question

I'm trying to create this huge hash, where there are many keys but only a few values.

So far I have it like so...

du_factor = {
  "A" => 1,
  "B" => 1,
  "C" => 1,
  "D" => 2,
  "E" => 2,
  "F" => 2,

...etc., etc., etc., on and on and on for longer than you even want to know. What's a shorter and more elegant way of creating this hash without flipping its structure entirely?

Edit: Hey so, I realized there was a waaaay easier and more elegant way to do this than the answers given. Just declare an empty hash, then declare some arrays with the keys you want, then use a for statement to insert them into the array, like so:

du1 = ["A", "B", "C"]
du2 = ["D", "E", "F"]

dufactor = {}

for i in du1
  dufactor[i] = 1
end

for i in du740
  dufactor[i] = 2
end

...but the fact that nobody suggested that makes me, the extreme Ruby n00b, think that there must be a reason why I shouldn't do it this way. Performance issues?

Answer 1

Combining Ranges with a case block might be another option (depending on the problem you are trying to solve):

case foo
when ('A'..'C') then 1
when ('D'..'E') then 2
# ...
end

Especially if you focus on your source code's readability.

Answer 2

How about:

vals_to_keys = {
  1 => [*'A'..'C'],
  2 => [*'D'..'F'],
  3 => [*'G'..'L'],
  4 => ['dog', 'cat', 'pig'],
  5 => [1,2,3,4]
}

vals_to_keys.each_with_object({}) { |(v,arr),h| arr.each { |k| h[k] = v } }
  #=> {"A"=>1, "B"=>1, "C"=>1, "D"=>2, "E"=>2, "F"=>2, "G"=>3, "H"=>3, "I"=>3,  
  #    "J"=>3, "K"=>3, "L"=>3, "dog"=>4, "cat"=>4, "pig"=>4, 1=>5, 2=>5, 3=>5, 4=>5}