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Discover how to efficiently plot multiple data files in Gnuplot and generate PNG outputs using a simple script.
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This video is based on the question https://stackoverflow.com/q/63015823/ asked by the user 'Mehdi' ( https://stackoverflow.com/u/13969917/ ) and on the answer https://stackoverflow.com/a/63023379/ provided by the user 'Ethan' ( https://stackoverflow.com/u/6797953/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Plot Multiple Files and Generate Outputs in Gnuplot

When working with data analysis, it's common to have multiple files containing time-series data that you need to visualize. If you're using Gnuplot, creating separate plots for each file can become tedious if done manually. Luckily, there's a way to automate this process, which saves you time and effort.

In this guide, we'll explore how to write a script in Gnuplot that allows you to plot multiple files and produce corresponding PNG outputs automatically. We will also incorporate a check to ensure that only existing data files are processed.

The Problem

You have a series of files named in the format file-%d, where %d represents the current date (like file-20200721, file-20200720, etc.). You want to plot all these files using a single Gnuplot script while saving the output PNG files with the same names as the input files (file-20200721.png).

You tried a basic script using a loop, but it didn't work as expected: it only produced one output file instead of one for each data file.

The Solution

Here’s how you can write a Gnuplot script to achieve that:

Step 1: Set Up the Graph Properties

First, configure the terminal and graphing properties. This includes setting the output format to PNG, defining the x-axis as time, and configuring the grid.

[[See Video to Reveal this Text or Code Snippet]]

Step 2: Loop Through Your Files

You will need to implement a loop that checks for the existence of each file before attempting to plot it. Here’s how you can write this loop:

[[See Video to Reveal this Text or Code Snippet]]

Explanation of the Code

The loop iterates through a predefined range of dates (in this case from 20200101 to 20200111).

For each iteration:

It constructs the input (fname_in) and output (fname_out) file names.

It tests if the input file exists using a shell command.

If the file does not exist, it prints a warning and continues to the next iteration.

If the file is found, it sets the PNG output file and plots the data.

Step 3: Run the Gnuplot Script

Once you have your script ready, run it in your terminal. It will automatically generate PNG files for each existing log file in the specified date range.

Conclusion

Using Gnuplot to visualize data from multiple files doesn't have to be a manual chore. With this automated approach, you can streamline your plotting process and generate PNG outputs based on existing data files quickly.

By following the steps outlined in this guide, you will be able to efficiently plot multiple files and ensure that each data file produces a corresponding output image without the hassle of checking each file manually.

Now, go ahead and make your data visualization tasks easier and more productive!