Looks like you are not dereferencing the followers hash :

my $followers = $data->{followersperdate}; ## just copy the reference 
+to the interesting part of the hash

** OR **

my %followers = %{ $data->{followersperdate} }; ## dereference the int
+eresting bit
[download]

See perlref for more details.

Other than for clarity this doesn't make much sense though, because you alredy have the data in a not-too-complex HoH, but you might want to look at Tie::Hash::Sorted, or just create an array of the hash keys in sorted order :

my @sorted_keys = 
  sort 
    { $data->{ followersperdate }->{ $b } 
      <=> 
    $data->{ followersperdate }->{ $a } } ## hi to lo on values
      keys %{ $data->{ followersperdate } }; ## again dereferencing as
+ above
[download]

Or you can directly access the contents this way, if you only need the sorted contents the once.
HTH.