[SOLVED] Getting user selected points from plotly and streamlit

Getting user selected points from plotly and streamlit

The following code outputs the selected points upon a user's selection:

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

# Sample data
df = px.data.iris()
# Note output of point selection fails if I uncomment the following line!?
# df = df.assign(sepal_width=np.random.randn(len(df)), sepal_length=np.random.randn(len(df)))


# Create a Plotly figure
fig = go.Figure()
fig.add_trace(go.Scatter(
    x=df['sepal_width'],
    y=df['sepal_length'],
    mode='markers',
))

# Display the figure with selection enabled
selected_points = st.plotly_chart(fig, on_select='rerun')

# Check if points are selected
st.write("Selected points:", selected_points)

# plotly.__version__==5.24.1
# st.__version__==1.42.2

However when I uncomment the df.assign line, it no longer does so! How can I make plotly+streamlit output the user selected data with my own data?

Solution

I believe this is happening because streamlit refreshes the page (and reruns your code) for every interaction, so if you don't set a random seed, the points will change every time you click on a data point.

If you set a random seed beforehand, then the functionality works:

np.random.seed(42)

df = px.data.iris()
df = df.assign(sepal_width=np.random.randn(len(df)), sepal_length=np.random.randn(len(df)))