foxplot

Plot time series from newline-delimited JSON.

Installation

pip install foxplot

Usage

Foxplot starts in interactive mode by default, which allows us to explore the input gathered in the data object (tab completion works: type data.<TAB> to explore) and plot times series from it using the fox.plot function:

$ foxplot upkie_2023-05-03-103245.mpack
Python 3.8.10 (default, Mar 13 2023, 10:26:41)
Type 'copyright', 'credits' or 'license' for more information
IPython 8.0.1 -- An enhanced Interactive Python. Type '?' for help.

In [1]: fox.plot(data.observation.imu.angular_velocity)

This call will open a new tab in your browser with a plot of the time series. In this example, angular_velocity is a 3D vector, thus the plot will include three curves.

Plotting from files

We can also plot data from files and pipes directly, for example:

• JSON: foxplot my_data.json -l /observation/cpu_temperature
• MessagePack: foxplot my_data.mpack -l /observation/cpu_temperature

Richer plot

Here is a more complex plot with both left- and right-axis time series:

In [2]: fox.plot(
   ...:     [
   ...:         data.observation.servo.left_knee.position,
   ...:         data.observation.servo.left_wheel.position,
   ...:     ],
   ...:     right=[
   ...:         data.observation.servo.left_knee.velocity,
   ...:         data.observation.servo.left_wheel.velocity,
   ...:     ],
   ...:     left_axis_unit="rad",
   ...:     right_axis_unit="rad/s",
   ...:     print_command_line=True,
   ...: )

This call will output a command line to directly reproduce the plot:

The command line to generate this plot is:

foxplot upkie_2023-05-03-103245.mpack -l /observation/servo/left_knee/torque /observation/servo/left_wheel/torque -r /observation/servo/left_knee/velocity /observation/servo/left_wheel/velocity

Check out the other arguments to fox.plot, for instance in the IPython shell by fox.plot?.

Tips

Zsh users can filter foxplot completion on JSON and MessagePack files:

zstyle ":completion:*:*:foxplot:*" ignored-patterns "^*.(json|mpack)"

See also

• µPlot's performance was a key enabler for this project.
• rq, a tool to manipulate streams of records in various formats.