publiplots.add_reference_line

publiplots.add_reference_line(ax, value, axis='y', color='red', linestyle='--', linewidth=1.5, alpha=0.7, label=None, zorder=1)[source]

Add a reference line to the plot.

Useful for showing thresholds, means, or other reference values. Internally calls axhline() (for axis='y') or axvline() (for axis='x').

Parameters:

  • ax (matplotlib.axes.Axes) – Axes to modify in place.

  • value (float) – Position of the reference line in data coordinates.

  • axis ({‘x’, ‘y’}, default 'y') – Which axis to add the line to: 'x' draws a vertical line at x=value; 'y' draws a horizontal line at y=value.

  • color (str, default 'red') – Line color.

  • linestyle (str, default '--') – Matplotlib linestyle spec.

  • linewidth (float, default 1.5) – Line width (points).

  • alpha (float, default 0.7) – Line transparency in [0, 1].

  • label (str, optional) – Label for the legend. None leaves the line unlabelled.

  • zorder (int, default 1) – Line z-order (higher values render on top).

Raises:

ValueError – If axis is not 'x' or 'y'.

Examples

Add horizontal reference line at y=0:

>>> pp.add_reference_line(ax, value=0, axis='y', label='Baseline')

Add vertical line at x=5:

>>> pp.add_reference_line(ax, value=5, axis='x', color='steelblue')