问题:

How do I turn an Array into a Hash with values of 0 without an each loop.

For example, given this array:

[1, 2, 3, 4]

I want to get this hash:

{"1"=>0, "2"=>0, "3"=>0, "4"=>0}

回答1:

I'm a fan of simple, and I can never remember exactly how crazy things #inject or Hash constructor arguments work.

array = [1, 2, 3, 4]
hash = {}

array.each do |obj|
  hash[obj.to_s] = 0
end

puts hash.inspect # {"1"=>0, "2"=>0, "3"=>0, "4"=>0}

The standard approach is Hash[...]:

Hash[xs.map { |x| [x.to_s, 0] }]

Or Enumerable#mash if you happen to use Facets. I cannot think of something more concise and declarative:

xs.mash { |x| [x.to_s, 0] }

array.inject({}) { | a, e | a[e.to_s] = 0; a }

or in a more clean way (thanks to tokland, see the discussion in the comments)

array.inject({}) { | a, e | a.update(e.to_s => 0) }

Okay, in reality, I'd use each_with_object, but posting this since it's more fun.

ary = *1..4

hash = Hash[ary.zip ary.dup.fill 0]

hash # => {1=>0, 2=>0, 3=>0, 4=>0}