Adding secondary y axis to bar line chart in ploty express

Question

I have a simple bar line chart. How can I add a secondary y-axis so I could show line chart (Column1) in a more representative way.

This is the code:

import pandas as pd
import dash
import plotly.express as px

data = [['A',100,880],['B ',50,450],['C',25,1200]]
df = pd.DataFrame(data,columns=['Letter','Column1','Column2'])
fig = px.line(x=df['Letter'], y=df['Column1'], color=px.Constant("Column1"),
             labels=dict(x="Letter", y="Column2", color="Legend"))
fig.add_bar(x=df['Letter'], y=df['Column2'], name="Letter")
fig.show()

Thanks in advance!

You can take a look to https://stackoverflow.com/q/62853539/12744275 — Renaud, May 05 '21 at 20:55

score 2 · Accepted Answer · answered May 05 '21 at 20:57

Per the plotly docs on multiple axis graphs:

Note: At this time, Plotly Express does not support multiple Y axes on a single figure. To make such a figure, use the make_subplots() function in conjunction with graph objects as documented below.

Here is a solution that uses the more fully-featured graph_objects:

import pandas as pd
import plotly.graph_objects as go
from plotly.subplots import make_subplots

data = [['A',100,880],['B ',50,450],['C',25,1200]]
df = pd.DataFrame(data,columns=['Letter','Column1','Column2'])

fig = make_subplots(specs=[[{"secondary_y": True}]])

fig.add_trace(
    go.Scatter(x=df['Letter'], y=df['Column1'], name="Column1", mode="lines"),
    secondary_y=True
)

fig.add_trace(
    go.Bar(x=df['Letter'], y=df['Column2'], name="Letter"),
    secondary_y=False
)

fig.update_xaxes(title_text="Letter")

# Set y-axes titles
fig.update_yaxes(title_text="Column2", secondary_y=False)
fig.update_yaxes(title_text="Column1", secondary_y=True)

fig.show()

which gives

As shown on the docs page linked above, there are multiple ways to achieve this which give you quite a bit of flexibility.

Though not officially supported, if you feel like you really need express you could try the answer offered on this SO post.

Adding secondary y axis to bar line chart in ploty express

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