It's quite impossible to change a hash-key, they are constant strings - strictly speaking they cannot even be numbers.

The string "465.274" is converted to a number when needed by perl, so that should not give you this warning, as the following code shows:

#!/usr/bin/perl -wl
use strict;

my @array = qw(465.274 21893.32 72.37); # qw creates quoted strings
print for (sort {$a <=> $b} @array);
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output:

72.37
465.274
21893.32
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No warnings at all.

Joost

-- 
#!/usr/bin/perl -np
BEGIN{@ARGV=$0}s(^([^=].*)|=)()s;
=Just another perl hacker\
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