You could just do:

%which_day = map { $_ => scalar split /,/, $cant_make_day{$_}} 
                        keys %cant_make_day;
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You should really be using strict and declaring your variables with my. This can save you headaches with misspelt names (see this node) Also you might want to use $elem rather than $elim (as it is short for element.

Hope this helps.

gav^