dynamic creation of hash

[MikeShank]

Hi,
How would I or is it possible to:

 file.each_line do |line|
    line_array = line.split("\t")
    line_array[0] = key
    line_array[1] = value
 # tried this, didnt work
    my_hash[key] = []
    my_hash[key] << value
 end 

What I'm looking to end up with is something like this:

 {"key1"=>["value1", "value1"]}
 {"key2"=>["value1", "value1", "value3", "value4"]}
 {"key3"=>["value1"]} 

thanks for any help