Plotly: How to set a fill color between two vertical lines?

Question

Using matplotlib, we can "trivially" fill the area between two vertical lines using fill_between() as in the example:

https://matplotlib.org/3.2.1/gallery/lines_bars_and_markers/fill_between_demo.html#selectively-marking-horizontal-regions-across-the-whole-axes

Using matplotlib, I can make what I need:

We have two signals, and I''m computing the rolling/moving Pearson's and Spearman's correlation. When the correlations go either below -0.5 or above 0.5, I want to shade the period (blue for Pearson's and orange for Spearman's). I also darken the weekends in gray in all plots.

However, I'm finding a hard time to accomplish the same using Plotly. And it will also be helpful to know how to do it between two horizontal lines.

Note that I'm using Plotly and Dash to speed up the visualization of several plots. Users asked for a more "dynamic type of thing." However, I'm not a GUI guy and cannot spend time on this, although I need to feed them with initial results.

BTW, I tried Bokeh in the past, and I gave up for some reason I cannot remember. Plotly looks good since I can use either from Python or R, which are my main development tools.

Thanks,

Carlos

Answer 1

I don't think there is any built-in Plotly method that that is equivalent to matplotlib's fill_between() method. However you can draw shapes so a possible workaround is to draw a grey rectangle and set the the parameter layer="below" so that the signal is still visible. You can also set the coordinates of the rectangle outside of your axis range to ensure the rectangle extends to the edges of the plot.

You can fill the area in between horizontal lines by drawing a rectangle and setting the axes ranges in a similar manner.

import numpy as np
import plotly.graph_objects as go

x = np.arange(0, 4 * np.pi, 0.01)
y = np.sin(x)

fig = go.Figure()
fig.add_trace(go.Scatter(
    x=x,
    y=y
))

# hard-code the axes
fig.update_xaxes(range=[0, 4 * np.pi])
fig.update_yaxes(range=[-1.2, 1.2])

# specify the corners of the rectangles
fig.update_layout(
    shapes=[
    dict(
        type="rect",
        xref="x",
        yref="y",
        x0="4",
        y0="-1.3",
        x1="5",
        y1="1.3",
        fillcolor="lightgray",
        opacity=0.4,
        line_width=0,
        layer="below"
    ),
    dict(
        type="rect",
        xref="x",
        yref="y",
        x0="9",
        y0="-1.3",
        x1="10",
        y1="1.3",
        fillcolor="lightgray",
        opacity=0.4,
        line_width=0,
        layer="below"
    ),
    ]
)

fig.show()