[rrd-users] Problems graphing

[Joshua Keroes]

See below

On Fri, Sep 26, 2008 at 8:05 AM, Laura McCord <mccordl at southwestern.edu>wrote:

> I have my data loaded into an array but everytime I try to graph the
> data I get a "Can't call method "png" on an undefined value...
>
> I am using Perl and the Graph module to produce a bar graph. Here is a
> sample of my data and my source code. Perhaps someone will notice what I
> am doing wrong.
>
> Thanks.
>
>
> Here is some sample data:
>
> Fri Sep 26 00:00:00 2008          0.1
> Fri Sep 26 01:00:00 2008          0.0
> Fri Sep 26 02:00:00 2008          0.1
> Fri Sep 26 03:00:00 2008          0.1
> Fri Sep 26 04:00:00 2008          0.2
> Fri Sep 26 05:00:00 2008          0.1
> Fri Sep 26 06:00:00 2008          0.2
> Fri Sep 26 07:00:00 2008          0.1
> Fri Sep 26 08:00:00 2008          0.2
> Fri Sep 26 09:00:00 2008          0.2
> Fri Sep 26 10:00:00 2008          0.2
>
> Here is a snippet of code:


# Got use strict; use warnings; in your code? They'll help.


>
>        #Every Hour
>       my $res = '60';
>
>       # Start on Sep 1st
>       my $start_t = "1220227200";


# This is really Aug 31

>
>       my $start_t_res = int($start_t/$res)*$res;


# And if you start to --start from this time, then you've just overflowed
time_t and you're trying to start at Wed Dec 31 15:59:59 1969, or time 0.


>
>       #End on Today's Date
>       my $end_t = "(int($start_t/$res)*$res)";


# unused. But you don't want to quote it anyway. That won't work.


>
>       my ($start,$step,$names,$data) =
> RRDs::fetch("stats.rrd","AVERAGE","-r","$res","-s",
> "$start_t_res","-e","now");


# see above about starting at wrong time.

>
>
>       print "Start:       ", scalar localtime($start), " ($start)\n";
>        print "Step size:   $step seconds\n";
>        print "DS names:    ", join (", ", @$names)."\n";
>        print "Data points: ", $#$data + 1, "\n";


# Try scalar @data here instead.

# Consider renaming @array1 to @timestamps and @array2 to @values or
# better: @whatever_those_values_actually_are. That makes it easier for
# us to read your code.
#
# There are faster ways to do this, but if it works, then I'll skip over it
for the most part.
# The only point I'll make is that if there are multiple DS's in your RRD,
then you'll
# only see the last one because the inner foreach loop will overwrite all of
the prior
# values in @line with just the last.
#

>        print "Data:\n";
>        foreach my $line (@$data) {
>               $start += $step;
>               $min++;
>                  #Here I am only loading hourly data into the array
>                  if($min == 60){
>                        $array1[$i] = localtime($start);
>                          foreach my $val (@$line) {
>                               $array2[$i] = $val;
>                           }
>                        $i++;
>                        $min=0;
>                  }
>        }
>
>       for($i=0;$i < @array1; $i++){
>               print $array1[$i]." ";
>               printf "%12.1f ", $array2[$i];
>               print "\n";
>       }


# I prefer something like this here:
#
# for my $i (0..$#timestamps) {
#     printf "$timestamps[$i]: %12.1f\n", $values[$i];
# }

      @actualdata = (\@array1,\@array2);


# Let's comment the above line out and ...


>
>       my $graph = new GD::Graph::bars;
>        $graph->set(
>           x_label         => 'Date/Time',
>           y_label         => 'Messages',
>           title           => 'Dropped Messages',
>           y_max_value     => 10,
>           y_tick_number   => 1,
>           y_label_skip    => 1,
>
>           # shadows
>           bar_spacing     => 10,
>           shadow_depth    => 4,
>           shadowclr       => 'dred',
>
>           transparent     => 0,
>       ) or warn $graph->error;
>

>       my $image = $graph->plot(\@actualdata)->png();

# ...move it down here where it's a little closer to the action thusly:
#
# my $image = $graph->plot( [\@timestamps, \@values] )->png;

Maybe that'll get you a little closer.

Good luck,
Joshua
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