Python Plotly – How to add multiple Y-axes?

In this article let’s see how to add multiple y-axes of different scales in Plotly charts in Python.

Currently, Plotly Express does not support multiple Y axes on a single figure. So, we shall use Plotly go. Plotly provides a function called make_subplots() to plot charts with multiple Y – axes. 

Syntax:

plotly.subplots.make_subplots(rows=1, cols=1, specs=None)

Parameter:

• rows: A number of rows in the subplot grid. (rows > 0). default 1
• cols: A number of columns in the subplot grid. (cols> 0). default 1
• specs: (list of lists of dict or None (default None)). Per subplot specifications of subplot type, row/column spanning, and spacing.

First, import the necessary functions from the Plotly package and create the secondary axes using the specs parameter in the make_subplots() function as shown. Plot a scatter plot with multiple y-axes. Make the chart readable by adding titles to the x and y axes.

Example: Adding 2 y-axis

Python3

# import graph_objects from plotly package
import plotly.graph_objects as go

# import make_subplots function from plotly.subplots
# to make grid of plots
from plotly.subplots import make_subplots

# use specs parameter in make_subplots function
# to create secondary y-axis
fig = make_subplots(specs=[[{"secondary_y": True}]])

# plot a scatter chart by specifying the x and y values
# Use add_trace function to specify secondary_y axes.
fig.add_trace(
    go.Scatter(x=[10, 20, 30], y=[400, 500, 600], name="yaxis values"),
    secondary_y=False)

# Use add_trace function and specify secondary_y axes = True.
fig.add_trace(
    go.Scatter(x=[20, 30, 40], y=[40, 50, 60], name="yaxis2 values"),
    secondary_y=True,)

# Adding title text to the figure
fig.update_layout(
    title_text="Multiple Y Axis in Plotly"
)

# Naming x-axis
fig.update_xaxes(title_text="X - axis")

# Naming y-axes
fig.update_yaxes(title_text="<b>Main</b> Y - axis ", secondary_y=False)
fig.update_yaxes(title_text="<b>secondary</b> Y - axis ", secondary_y=True)

 Output:

Plotly scatter plot with multiple y-axes

Example: Adding 2 y-axis 

Python3

# import graph_objects from plotly package
import plotly.graph_objects as go

# import make_subplots function from plotly.subplots
# to make grid of plots
from plotly.subplots import make_subplots

# use specs parameter in make_subplots function
# to create secondary y-axis
fig = make_subplots(specs=[[{"secondary_y": True}]])

# plot a bar chart by specifying the x and y values
# Use add_trace function to specify secondary_y axes.
fig.add_trace(
    go.Bar(x=[10, 20, 30], y=[40, 50, 60], name="yaxis values"),
    secondary_y=False)

# Use add_trace function and specify secondary_y axes = True.
fig.add_trace(
    go.Bar(x=[20, 30, 40], y=[400, 500, 600], name="yaxis2 values"),
    secondary_y=True,)

# Adding title text to the figure
fig.update_layout(
    title_text="Multiple Y Axis in Plotly"
)

# Naming x-axis
fig.update_xaxes(title_text="X - axis")

# Naming y-axes
fig.update_yaxes(title_text="<b>Main</b> Y - axis ", secondary_y=False)
fig.update_yaxes(title_text="<b>secondary</b> Y - axis ", secondary_y=True)

Output:

Plotly bar chart with multiple y axes

Plotly chart with multiple Y – axes 

Now, let us look at how to plot a scatter chart with more than 2 Y-axes or multiple Y-axis. The procedure is the same as above, the change comes in the figure layout part to make the chart more visually pleasing.

Import the necessary functions from the Plotly package. Create the secondary axes using the specs parameter in the make_subplots function as shown. Plot a scatter plot with multiple y-axes.

Example: Adding more than multiple y-axis

Python3

# import the graph_objects function from
# plotly package
import plotly.graph_objects as go

# initialize a Figure object and store it in
# a variable fig
fig = go.Figure()

# add x and y values for the 1st scatter
# plot and name the yaxis as yaxis1 values
fig.add_trace(go.Scatter(
    x=[10, 12, 13],
    y=[41, 58, 60],
    name="yaxis1 values"
))

# add x and y values for the 2nd scatter
# plot and name the yaxis as yaxis2 values
fig.add_trace(go.Scatter(
    x=[12, 13, 14],
    y=[401, 501, 610],
    name="yaxis2 values",
    yaxis="y2"
))

# add x and y values for the 3rd scatter
# plot and name the yaxis as yaxis3 values
fig.add_trace(go.Scatter(
    x=[14, 15, 16],
    y=[42000, 53000, 65000],
    name="yaxis3 values",
    yaxis="y3"
))

# add x and y values for the 4th scatter plot
# and name the yaxis as yaxis4 values
fig.add_trace(go.Scatter(
    x=[15, 16, 17],
    y=[2000, 5000, 7000],
    name="yaxis4 values",
    yaxis="y4"
))

# Create axis objects
fig.update_layout(
    # split the x-axis to fraction of plots in
    # proportions
    xaxis=dict(
        domain=[0.3, 0.7]
    ),

    # pass the y-axis title, titlefont, color
    # and tickfont as a dictionary and store
    # it an variable yaxis
    yaxis=dict(
        title="yaxis 1",
        titlefont=dict(
            color="#0000ff"
        ),
        tickfont=dict(
            color="#0000ff"
        )
    ),

    # pass the y-axis 2 title, titlefont, color and
    # tickfont as a dictionary and store it an
    # variable yaxis 2
    yaxis2=dict(
        title="yaxis 2",
        titlefont=dict(
            color="#FF0000"
        ),
        tickfont=dict(
            color="#FF0000"
        ),
        anchor="free",  # specifying x - axis has to be the fixed
        overlaying="y",  # specifyinfg y - axis has to be separated
        side="left",  # specifying the side the axis should be present
        position=0.2  # specifying the position of the axis
    ),

    # pass the y-axis 3 title, titlefont, color and
    # tickfont as a dictionary and store it an
    # variable yaxis 3
    yaxis3=dict(
        title="yaxis 3",
        titlefont=dict(
            color="#006400"
        ),
        tickfont=dict(
            color="#006400"
        ),
        anchor="x",     # specifying x - axis has to be the fixed
        overlaying="y",  # specifyinfg y - axis has to be separated
        side="right"  # specifying the side the axis should be present
    ),

    # pass the y-axis 4 title, titlefont, color and
    # tickfont as a dictionary and store it an
    # variable yaxis 4
    yaxis4=dict(
        title="yaxis 4",
        titlefont=dict(
            color="#8f00ff"
        ),
        tickfont=dict(
            color="#8f00ff"
        ),
        anchor="free",  # specifying x - axis has to be the fixed
        overlaying="y",  # specifyinfg y - axis has to be separated
        side="right",  # specifying the side the axis should be present
        position=0.8  # specifying the position of the axis
    )
)


# Update layout of the plot namely title_text, width
# and place it in the center using title_x parameter
# as shown
fig.update_layout(
    title_text="4 y-axes scatter plot in plotly",
    width=1000,
    title_x=0.5
)

Output:

Plotly scatter plot with multiple y – axes