# How do I declare a hash of hashes of numbers in Perl 6?

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Category：Languages

A hash, by default, converts all keys to strings. This causes issues when your keys are numbers which may be close:

``> my %h; %h{1/3} = 1; %h{0.333333} = 2; dd %h; Hash %h = {"0.333333" => 2} ``

This can, of course, be fixed as follows:

``>  my %h{Real}; %h{1/3} = 1; %h{0.333333} = 2; dd %h; Hash[Any,Real] %h = (my Any %{Real} = 0.333333 => 2, <1/3> => 1) ``

But now I need a hash of hashes of numbers, e.g. `{ 1/3 => { 2/3 => 1, 0.666667 => 2 } }`.

``> my %h{Real}; %h{1/3}{2/3} = 1; %h{1/3}{0.666667} = 2; dd %h; Hash[Any,Real] %h = (my Any %{Real} = <1/3> => \${"0.666667" => 2}) ``

How do I fix that?

Best I can figure out is the following workaround:

``> my %h{Real}; %h{1/3} //= my %{Real}; %h{1/3}{2/3} = 1; %h{1/3}{0.666667} = 2; dd %h; Hash[Any,Real] %h = (my Any %{Real} = <1/3> => \$(my Any %{Real} = <2/3> => 1, 0.666667 => 2)) ``

but that's just annoying.

The following works:

``my Hash[Real,Real] %h{Real}; %h{1/3} .= new; %h{1/3}{2/3} = 1; ``

Which is not great.

The following also works as a work-around.

``my Hash[Real,Real] %h{Real}; %h does role {   method AT-KEY (|) is raw {     my /result = callsame;     result .= new unless defined result;     result   } }  %h{1/3}{2/3} = 1;  say %h{1/3}{2/3}; # 1 ``

If you have more than one such variable:

``role Auto-Instantiate {   method AT-KEY (|) is raw {     my /result = callsame;     result .= new unless defined result;     result   } }  my Hash[Real,Real] %h{Real} does Auto-Instantiate; ``