ruby - Swapping keys and values in a hash -

in ruby, how swap keys , values on hash?

let's have following hash:

{:a=>:one, :b=>:two, :c=>:three} 

that want transform into:

{:one=>:a, :two=>:b, :three=>:c} 

using map seems rather tedious. there shorter solution?

ruby has helper method hash lets treat hash if inverted.

{a: 1, b: 2, c: 3}.key(1) => :a 

if want keep inverted hash, hash#invert should work situations.

{a: 1, b: 2, c: 3}.invert => {1=>:a, 2=>:b, 3=>:c} 

but...

if have duplicate values, invert discarding last of values. likewise key return first match.

{a: 1, b: 2, c: 2}.key(2) => :b  {a: 1, b: 2, c: 2}.invert => {1=>:a, 2=>:c} 

so.. if values unique can use hash#invert if not, can keep values array, this:

class hash   # invert not lossy   # {"one"=>1,"two"=>2, "1"=>1, "2"=>2}.inverse => {1=>["one", "1"], 2=>["two", "2"]}    def safe_invert     each_with_object({}) |(key,value),out|        out[value] ||= []       out[value] << key     end   end end 

note: code tests here.

or in short...

class hash   def safe_invert     self.each_with_object({}){|(k,v),o|(o[v]||=[])<<k}   end end