[Bioperl-l] Bio::Graphics sort_order

[Richard Adams]

Hello,
    I'm trying to sort the display order  of features based on values
in  one of the features' tags using the syntax
    described in the Bio::Graphics::Panel :doc.
        i.e.,
sort_order =>    sub {(  ($a->each_tag_value('Conserved'))[0]
<=>($b->each_tag_value('Conserved'))[0]  )};
But I get the error message
"Can't call method "each_tag_value" on an undefined value at
Draw_Output.pm". The code doesn't seem to be
recognizing that $a and $b should refer to the features. I've tried
delving into the internal workings of Bio::Graphics::Glyph::Factory
with little enlightenment, would be grateful for any ideas.
Cheers
Richard


--
Dr Richard Adams
Bioinformatician,
Psychiatric Genetics Group,
Medical Genetics,
Molecular Medicine Centre,
Western General Hospital,
Crewe Rd West,
Edinburgh UK
EH4 2XU

Tel: 44 131 651 1084
richard.adams at ed.ac.uk