Re: sorting scientific numbers

Chances are good that by virtue of how the numeric data is getting into your script, Perl is seeing '1e-13' as a string, not a number. You can see this happening here:

perl -e "print q/2e+11/, $/; print 2e+11, $/;"
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You can coerce it back to a number by treating it like one. One way is by adding zero to it:

perl -e "print q/2e+11/ + 0, $/;"
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And here is that theory applied to an example that may more closely resemble your problem code.

my @numbers;
while( my $num = <DATA> ) {
    chomp $num;
    push @numbers, $num + 0;
}
print "$_\n" for sort { $a <=> $b } @numbers;
__DATA__
1e-13
2e-18
1e-11
[download]

I hope this is on the right track. ;)

Dave

Comment on Re: sorting scientific numbers Select or Download Code

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Re^2: sorting scientific numbers by kaif (Friar) on Jun 08, 2005 at 07:57 UTC
That's a good theory, but the spaceship operator `$a <=> $b` coerces its argument into ~~integers~~ numbers, so this shouldn't matter. Indeed, run your code without the `+ 0` or simply `perl -le'$,="\n"; print sort {$a<=>$b} qw(1e-13 2e-18 1e-11)'` [download] and you will see that the output is the same.	[reply] [d/l] [select]
Re^2: sorting scientific numbers by tlm (Prior) on Jun 08, 2005 at 12:31 UTC
This is somewhat tangetial, but in a numerical context perl will coerce any string that begins with something recognizable as a number into a number. That's why "0 but true" is a perfectly good¹ "true zero." See Is '2x' + '3y' == 5 documented? and the man page for the C `atof` function. ¹Well, not quite. As it turns out `'0 but true'` has a "special dispensation" that disables the warnings that perl would have otherwise have generated. E.g.: `% perl -wle 'print "OK" if "0 but true" < 1' OK % perl -wle 'print "OK" if "0 but righteous" < 1' Argument "0 but righteous" isn't numeric in numeric lt (<) at -e line +1. OK` [download] the lowliest monk	[reply] [d/l]