Using Perl script to create flat file

[PS]

Hi,

I am using convertProbesetCSV_differentInput.pl file (http://www.aroma-project.org/share/scripts/third-party/archive/20090212/convertProbesetCSV_differentInput.plhttp://www.aroma-project.org/share/scripts/third-party/archive/20090212/convertProbesetCSV_differentInput.pl)  for creating a flat file. My probe.tab file probe name like "Zm020985_at_10". When I run the perl script, I got an error ;

Argument "Zm020985_at" isn't numeric in numeric comparison (<=>) at convertProbesetCSV_differentInput.pl line 96.

Since I am beginner at Perl, I got confused in script at line 96 and 97.

sub by_number { $a <=> $b}

my @orderedKeys=sort by_number keys %probes;

How do I overcome this error? Please help.

Thanking you in advance.

Regards,

PS