Ruby foo: flatten a hash into a string

Flatten a ruby hash into a string. In this case the comma is the key value delimiter and the semicolon is the entry delimiter.

irb(main):016:0> a={'sdfs'=>['aaa','bbb'], 'ppp'=>['aa','a']}
=> {"ppp"=>["aa", "a"], "sdfs"=>["aaa", "bbb"]}
=> ["ppp:aa,a", "sdfs:aaa,bbb"]
irb(main):018:0> b=a.map { |k, v| "#{k}:#{v.join(',')}" }.join(";")
=> "ppp:aa,a;sdfs:aaa,bbb"