Question about using hash indexes with GD::Graph

[vonman]

I am trying to use the GD::Graph module to plot a chart that will have militay hour number on the x-axis and a count on the y-axis. I have indexes for my hash table for 'hour' and 'count'. I would like to use the GD::Graph::lines function. Below is the example code that I am trying to plot my data but it gives me errors.

# This is the original data from the perldoc examples
# @data=(["1st","2nd","3rd"],
#        [9,4,7]);


#  I have a hash table with $data[$index]{'hour'} and $data[$index]{'c
+ount'}
#
$graph= GD::Graph::lines->new(400,300);
$graph->set(
    x_label => 'Hour',
    y_label => 'Transaction Volume',
    title => 'Number of transactions per hour',
    y_max_value => 20,
    y_label_skip => 1,
    y_tick_number => 1);

    $gd = $graph->plot(\@data);

    open (IMG,'>file.png') or die $!;
    binmode IMG;
    print IMG $gd->png;
    close IMG;

Any ideas? Thanks in advance!!

[jeffa]

UPDATE: see comments

How about:

my (@h,@c);
push @h, $_->{hour} foreach(@{$data});   # no so great
push @c, $_->{count} foreach(@{$data});  # see extremely's comment 
my $new = [ \@h, \@c ];

$gd = $graph->plot($new);                # wrong - see orbital's comme
+nt

I really tried to avoid the temp lists, maybe someone will come along and make this puppy scream with a nasty map block. ;)

BEFORE:                          AFTER:
$VAR1 = [                        $VAR1 = [
          {                                [  
            'count' => 5,                     1,
            'hour' => 1                       5,
          },                                  2
          {                                ],
            'count' => 2,                  [
            'hour' => 5                       5,
          },                                  2,
          {                                   8
            'count' => 8,                  ]  
            'hour' => 2                  ];
          }
        ];

Data::Dumper - don't code anonymous data structures without it.

Jeff

R-R-R--R-R-R--R-R-R--R-R-R--R-R-R--
L-L--L-L--L-L--L-L--L-L--L-L--L-L--

[extremely]

merlyn showed ya map but honestly you shouldn't get into the habit of traipsing through a data set multiple times. When ever you see two lines that both end "foreach (@array)" you should be doing:

foreach (@data) {
push @h, $_->{'hour'};
push @c, $_->{'count');
}

You get in a hurry and do it wrong then wind up going through the same data like 7 or 8 times when there are 100,000 items in the list and you are going start wondering where your afternoon of surfing PM went. =P

--
$you = new YOU;
honk() if $you->love(perl)

[vonman]

This is perfect except that I had to cange the foreach lines to look like follows.

my (@h,@c);
push @h, $_->{'hour'} foreach(@data);
push @c, $_->{'count'} foreach(@data);
my $new = [ \@h, \@c];

Now it is graphing correctly

[merlyn]

Any kind of push @x, .... for @y should immediately invoke that magic three-letter word, "m a p".

my $new = [ [map $_->{hour}, @data], [map $_->{count}, @data] ];

-- Randal L. Schwartz, Perl hacker

[orbital]

I still don't think that will solve the problem of the error. I would agree with jeffa on how to format your data but your 2nd to the last line I think is what is hanging you up. This is my suggestion:

print IMG $gd->plot(\@data)->png;

[vonman]

You are correct the error message that I am receiving is

Can't call method "png" on an undefined value at _graph_test.pl line 9
+1, <STDIN> line 1.

[vonman]

I am still running into trouble with the data. I have changed the code to read like follows

my (@h,@c);
push @h, $_->{'hour'} foreach(@{$data});
push @c, $_->{'count'} foreach(@{$data});
my $new = [ \@h, \@c];
print (\@new);


#@data=(["1st","2nd","3rd"],
#        [9,4,7]);


#  I have a hash table with $data[$index]{'hour'} and $data[$index]{'c
+ount'}
#
$graph= GD::Graph::lines->new(400,300);
$graph->set(
    x_label => 'Hour',
    y_label => 'Transaction Volume',
    title => 'Number of transactions per hour',
    y_max_value => 20,
    y_label_skip => 1,
    y_tick_number => 1);

    #$gd = $graph->plot(\@data);

    open (IMG,'>file.png') or die $!;
    binmode IMG;
    print IMG $graph->plot(\@new)->png;

    close IMG;

but when I run it I still receive the same error. If I uncomment the @data lines and plot to @data instead of @new it works. Any ideas?

[orbital]

because $new is an array reference, so all you need to do is fill it in as $graph->plot($new)->png;

[arturo]

$new is a already a reference to an array consisting of two arrayrefs. There is no such thing (yet) as @new in the code snippet you've posted. Try it with

print IMG $graph->plot($new)->png;

(instead of the \@new you have there now) and see what happens.

use strict should have caught this. You *are* using, strict, aren't you?

Philosophy can be made out of anything. Or less -- Jerry A. Fodor