Graphics::Skullplot - Plot the result of an SQL select (e.g. from an emacs shell window)


Version 0.01


   # To use this from emacs, see scripts/skullplot.el.
   # That elisp code accesses the perl script: scripts/

   # the code used by
   my $plot_hints = { indie_count           => $indie_count,
                      dependent_requested   => $dependent_requested,
                      independent_requested => $independent_requested,
   my %gsp_args = 
     ( input_file   => $dbox_file,
       plot_hints   => $plot_hints, );
   $gsp_args{ working_area } = $working_area if $working_area;
   $gsp_args{ image_viewer } = $image_viewer if $image_viewer;
   my $gsp = Graphics::Skullplot->new( %gsp_args );

   $gsp->show_plot_and_exit();  # does an exec 


Graphics::Skullplot is a module that works with the result from a database select in the common tabular text "data box" format. It has routines to generate and display plots of the data in png format.

Internally it uses the Table::BoxFormat module to parse the text table, and the Graphics::Skullplot::ClassifyColumns module to determine the types of the columns.

The default image viewer is the ImageMagick "display" command.

The immediate use for this code is to act as the back-end for the included Emacs package scripts/skullplot.el, so that database select results generated in an emacs shell window can be immediately plotted.

This elisp code calls scripts/, which might be used in other contexts.



Creates a new Graphics::Skullplot object. Object attributes:


Scratch location where intermediate files are created. Defaults to "/tmp".


Defaults to 'display', the ImageMagick viewer (a dependency on Image::Magick ensures it's available)

builder methods (largely for internal use)

builder_image_viewer Currently just returns a hardcoded selection (the ImageMagick "display" program).


Example usage:

  # relies on object settings: "input_file" and "working area"
  my $fn = 
  my $basename = $fn->{ base };
  # full paths to file in $working_area
  my $tsv_file  = $fn->{ tsv };  
  my $png_file  = $fn->{ png };  

Generate the r-code to plot the tsv file data as the png file. Takes one argument, a hash of "field metadata".

The file names (tsv, png, plus internal formats) come from the "naming" object field.

Example usages:

  $self->plot_tsv_to_png( $plot_cols ); 

Example usage:

  $self->generate_png_file( $pc, $fn );

Runs the given plot code (first argument) using the file-name metadata (second argument, defaults to object's naming), saving the plot as a png file ($fn->{png}).

This generates a file of R code to run with an Rscript call. In debug mode, this generates a standalone unix script. ($DEBUG).


Open the given png file in an image viewer Defaults to "png" field in object's "naming".

This internally does an exec: it should be the last thing called.

The image viewer can be set as the second, optional field. The default image viewer is ImageMagick's "display".

Example usage:

  my $naming = $self->naming;
  my $png_file = $naming->{ png };
  $self->display_png_and_exit( $png_file );

The method called by the script to actually plot the data from a "data box format" file, using the plot_hints.

It's expected that the dbox file (input_file) and the plot_hints will be defined at object creation, but at present those settings may be overridden here and given as first and second arguments.

This should be used at the end of the program (internally it does an "exec").


Given a reference to the tabular data in the form of an array of arrays, returns metadata for each column to be used in deciding how to plot the data.

Example usage:

  my $plot_cols = $self->classify_columns( $data );

Classify the columns from the tabular data, returning a "fields_metadata" hash ref.

This is a wrapper around a provisional technique to make it easier to swap in better ones later.

At present, the metadata fields are:

     x           => $x_field  (( rename indie_x ))
     y           => $y_field
     gb_cats      => [ @gb_cats ]
     dependents_y => [ @dependents_y ]

Report on state of object fields.




  • Limited to two group by categories (in addition to the x-axis): used with colour & shape If there's more than 2, fuse them together into a compound, use with colour

  • See R Graphics Cookbook, p.205: setting up the tics and labels.

        $pc .= 'p + scale_x_date';
        $pc .= '';
  • Currently this defaults to viewing images using the "display" program. Alternately, the builder_image_viewer could scan through a list of likely viewers and pick the first that's installed.


Joseph Brenner, <>, 16 Nov 2016


Copyright (C) 2016 by Joseph Brenner

This program is free software; you can redistribute it and/or modify it under the terms of either: the GNU General Public License as published by the Free Software Foundation; or the Artistic License.

See for more information.