Philipp K. Janert - Gnuplot in Action: Understanding Data with Graphs

1. Color With gnuplot 5, color is the way to go. It is no longer an afterthought and, moreover, it is no longer optional: gnuplot 5 assumes that you are creating color graphs. Monochrome is now a special case.

2. Color scheme Gnuplot 5 uses a new default color sequence; you can get the old one back using the command: set colorsequence classic.

3. Consistency across terminals Using gnuplot 5, you can generate output in all common formats (that is, PDF, PNG, and for the screen) using a consistent set of routines (or "terminals"), all built on the Cairo graphics libraries. The differences among terminals for various output formats are now largely a thing of the past.

4. Better terminals Terminals are not only more consistent, they are also much better and generally more powerful. Text handling in particular is much improved, with enhanced text mode now the default mode for contemporary terminals.

5. PDF The standard print-quality output format is now PDF, not Postscript anymore.

6. Unicode and UTF-8 Gnuplot 5 understands UTF-8 encoded Unicode. This may sound like a nuisance, but it is, in fact, a tremendous improvement. You can now use almost any character in a string or text label, and do so in a straightforward and consistent manner. (I explain all this in chapter 5.)

7. Loops Gnuplot 5 includes support for some labor-saving features that can speed up repetitive tasks. It is now possible to automate a series of plot or set commands through inline loops.

8. More consistent styles The handling of line and point styles has become more consistent and powerful.

• Based on your local configuration, the graphs that you see when you type in commands at your own computer may look somewhat different from the figures in the book. Do not be disturbed if colors or point types look differentthese are merely configuration details! The overall content of the figure should always be the same as in the book.

• Gnuplot's plot command requires the name of a file with data to be present. Example graphs of many actual data files are presented in this book (and the files will, eventually, also be available for download). Whenever I show the plot command for an actual data file, I will use the proper file name in the plot command, like so:

  plot "prices" using 1:2 with lines

  But at other times, I only want to demonstrate the syntax of the plot command. In these cases, there is no data file, and I use the generic file name "data" as a placeholder. Hence, whenever you see the file name "data", you know that this command is only there to illustrate the surrounding discussion. This will always be clear from the context; in any case, I never use the name "data" for an actual data file.

This chapter covers:

Gnuplot is probably the most widely used open source program for plotting and visualizing data. In this book, I want to show you how to use gnuplot to make plots and graphs of your data: both quick and easy graphs for your own use and highly polished graphs for presentations and publications.

But I also want to show you something else: how to solve data analysis problems using graphical methods. The art of discovering relationships in data and extracting information from it by visual means is called graphical analysis and I believe gnuplot to be an excellent tool for it.