Plotly: How To Set A Fill Color Between Two Vertical Lines?

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/fi

Solution 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()

Solution 2:

You haven't provided a data sample so I'm going to use a synthetical time-series to show you how you can add a number of shapes with defined start and stop dates for several different categories using a custom function bgLevel

---

Two vertical lines with a fill between them very quickly turns into a rectangle. And rectangles can easily be added as shapes using fig.add_shape. The example below will show you how to find start and stop dates for periods given by a certain critera. In your case these criteria are whether or not the value of a variable is higher or lower than a certain level.

Using shapes instead of traces with fig.add_trace() will let you define the position with regards to plot layers using layer='below'. And the shapes outlines can easily be hidden using line=dict(color="rgba(0,0,0,0)).

Plot 1: Time series figure with random data:

Plot 2: Background is set to an opaque grey when A > 100 :

Plot 2: Background is also set to an opaque red when D < 60

Complete code:

import numpy as np
import pandas as pd
import plotly.graph_objects as go
import plotly.express as px
import datetime

pd.set_option('display.max_rows', None)

# data sample
nperiods = 200
np.random.seed(123)
df = pd.DataFrame(np.random.randint(-10, 12, size=(nperiods, 4)),
                  columns=list('ABCD'))
datelist = pd.date_range(datetime.datetime(2020, 1, 1).strftime('%Y-%m-%d'),periods=nperiods).tolist()
df['dates'] = datelist 
df = df.set_index(['dates'])
df.index = pd.to_datetime(df.index)
df.iloc[0] = 0
df = df.cumsum().reset_index()

# function to set background color for a# specified variable and a specified level# plotly setup
fig = px.line(df, x='dates', y=df.columns[1:])
fig.update_xaxes(showgrid=True, gridwidth=1, gridcolor='rgba(0,0,255,0.1)')
fig.update_yaxes(showgrid=True, gridwidth=1, gridcolor='rgba(0,0,255,0.1)')

defbgLevels(fig, variable, level, mode, fillcolor, layer):
    """
    Set a specified color as background for given
    levels of a specified variable using a shape.
    
    Keyword arguments:
    ==================
    fig -- plotly figure
    variable -- column name in a pandas dataframe
    level -- int or float
    mode -- set threshold above or below
    fillcolor -- any color type that plotly can handle
    layer -- position of shape in plotly fiugre, like "below"
    
    """if mode == 'above':
        m = df[variable].gt(level)
    
    if mode == 'below':
        m = df[variable].lt(level)
        
    df1 = df[m].groupby((~m).cumsum())['dates'].agg(['first','last'])

    for index, row in df1.iterrows():
        #print(row['first'], row['last'])
        fig.add_shape(type="rect",
                        xref="x",
                        yref="paper",
                        x0=row['first'],
                        y0=0,
                        x1=row['last'],
                        y1=1,
                        line=dict(color="rgba(0,0,0,0)",width=3,),
                        fillcolor=fillcolor,
                        layer=layer) 
    return(fig)

fig = bgLevels(fig = fig, variable = 'A', level = 100, mode = 'above',
               fillcolor = 'rgba(100,100,100,0.2)', layer = 'below')

fig = bgLevels(fig = fig, variable = 'D', level = -60, mode = 'below',
               fillcolor = 'rgba(255,0,0,0.2)', layer = 'below')

fig.show()