Mapping the keys of a Hash

I am working with a hash called `my_hash`: ``` { "2011-02-01 00:00:00+00" => 816, "2011-01-01 00:00:00+00" => 58, "2011-03-01 00:00:00+00" => 241 } ``` My aim is to get rid of the “00:00:00+00” at the end of all the keys, resulting in this hash: ``` { "2011-02-01" => 816, "2011-01-01" => 58, "2011-03-01" => 241 } ``` What I tried First, I try to parse all the keys in `my_hash` (which are timestamps). ``` my_hash.keys.sort.each do |key| parsed_keys << Date.parse(key).to_s end ``` Which gives me this: ``` ["2011-01-01", "2011-02-01", "2011-03-01"] ``` Then, I try to map `parsed_keys` back to the keys of `my_hash`: ``` Hash[my_hash.map {|k,v| [parsed_keys[k], v]}] ``` But that returns the following error: ``` TypeError: can't convert String into Integer ``` How can I map `parsed_keys` back to the keys of `my_hash`?