How to avoid Plotly (plotly.express.line) line chart creating zig-zag line?

Question

I want to create line charts with plotly, my X axis is a year, y a value. Sometimes, the data is incomplete, i.e., some curves will have years missing or will start in different years than others.

It appears this can lead to zig-zag lines where I would expect the lines to be connected in the order the data is provided.

Here's a simple example:

#!/usr/bin/python3
import plotly.express
curve_a = {2010: 20, 2011: 21, 2012: 22, 2014: 22, 2015: 23}
curve_b = {2009: 18, 2010: 21, 2011: 22, 2012: 23, 2013: 21, 2014: 21, 2015: 20}
dat = {"A": curve_a, "B": curve_b}
fig = plotly.express.line(dat, markers=True)
fig.show()

Here's how it looks:

As you can see, the red line starts at 2010, and jumps to 2009 and 2013 at the end.

I can workaround this by adding a fake line at the bottom that spans the whole range and is used as the first in the dataset, but that's, of course, not a very good solution.

Any help appreciated.

0stone0 · Accepted Answer · 2025-11-17 13:23:20Z

1

The issue is caused by plotly not sorting the dates/years by itself so you get a 'zigzag' line.

Easiest way is to use the sort_index function from pandas to sort your indexes (years):

dat = pd.DataFrame(dat).sort_index()

Gives:

Full code:

import plotly.express as px
import pandas as pd

curve_a = {2010: 20, 2011: 21, 2012: 22, 2014: 22, 2015: 23}
curve_b = {2009: 18, 2010: 21, 2011: 22, 2012: 23, 2013: 21, 2014: 21, 2015: 20}
dat = {"A": curve_a, "B": curve_b}
dat = pd.DataFrame(dat).sort_index()

fig = px.line(dat, x=dat.index, y=dat.columns, markers=True)
fig.show()

answered 2 days ago

0stone0

45.5k6 gold badges53 silver badges82 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

PV8 · Accepted Answer · 2025-11-17 13:16:53Z

You can create an x-axis with the full year-list:

import pandas as pd
import plotly.express as px

curve_a = {2010: 20, 2011: 21, 2012: 22, 2014: 22, 2015: 23}
curve_b = {2009: 18, 2010: 21, 2011: 22, 2012: 23, 2013: 21, 2014: 21, 2015: 20}

# Create DataFrame from both curves
df = pd.DataFrame({'A': curve_a, 'B': curve_b})

# Create a complete year index
all_years = range(min(df.index.min(), df.index.min()), max(df.index.max(), df.index.max()) + 1)
df = df.reindex(all_years)

# Melt for plotly express
df = df.reset_index().melt(id_vars='index', var_name='curve', value_name='value')
df.rename(columns={'index': 'year'}, inplace=True)

fig = px.line(df, x='year', y='value', color='curve', markers=True)
fig.show()

Collectives™ on Stack Overflow

How to avoid Plotly (plotly.express.line) line chart creating zig-zag line?

2 Answers 2

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related