How to plot a colored gantt chart with plotly keeping the correct bar height

Question

I have the following code to plot a gantt chart in plotly:

import datetime
import pandas
import plotly.express as px

task_list = [{
    'Task': 'T-3', 'y': 0, 'Start': datetime.date(2022, 2, 24),
    'Finish': datetime.date(2022, 3, 17), 'Status': 'Scheduled'}, {
    'Task': 'SNP-350', 'y': 1, 'Start': datetime.date(2022, 2, 24),
    'Finish': datetime.date(2022, 2, 25), 'Status': 'Backlog'}, {
    'Task': 'RD-6687', 'y': 2, 'Start': datetime.date(2022, 3, 18),
    'Finish': datetime.date(2022, 4, 8), 'Status': 'Selected'}, {
    'Task': 'RD-6643', 'y': 3, 'Start': datetime.date(2022, 2, 24),
    'Finish': datetime.date(2022, 3, 17), 'Status': 'Scheduled'}, {
    'Task': 'SNP-337', 'y': 4, 'Start': datetime.date(2022, 5, 21),
    'Finish': datetime.date(2022, 5, 23), 'Status': 'Backlog'}, {
    'Task': 'SNP-352', 'y': 5, 'Start': datetime.date(2022, 2, 26),
    'Finish': datetime.date(2022, 2, 28), 'Status': 'Clarification'}, {
    'Task': 'SNP-239', 'y': 6, 'Start': datetime.date(2022, 5, 24),
    'Finish': datetime.date(2022, 5, 25), 'Status': 'Selected'}]

df = pandas.DataFrame(task_list)

fig = px.timeline(df, x_start="Start", x_end="Finish", y="y",
                  # color="Status",
                  )

fig.show()

This gives me a gantt chart as expected:

However, if I now include the line that is commented out in the code above, i.e. color the bars in the gantt chart according to their status, it messes up the height of the different bars:

So the colors are shown as expected but it seems the height of the different bars is now not limited by the neighboring bar but only by the neighboring bar with the same color. How can I add the colors to the gantt chart but keep the height of the bars as it is without colors?

Answer 1

• using color creates a trace for each Status, hence change in heights
• have put Status into hover_data
• built colormap and then updated trace to use value of Status to lookup color

import datetime
import pandas
import plotly.express as px
import numpy as np

# fmt: off
task_list = [{
    'Task': 'T-3', 'y': 0, 'Start': datetime.date(2022, 2, 24),
    'Finish': datetime.date(2022, 3, 17), 'Status': 'Scheduled'}, {
    'Task': 'SNP-350', 'y': 1, 'Start': datetime.date(2022, 2, 24),
    'Finish': datetime.date(2022, 2, 25), 'Status': 'Backlog'}, {
    'Task': 'RD-6687', 'y': 2, 'Start': datetime.date(2022, 3, 18),
    'Finish': datetime.date(2022, 4, 8), 'Status': 'Selected'}, {
    'Task': 'RD-6643', 'y': 3, 'Start': datetime.date(2022, 2, 24),
    'Finish': datetime.date(2022, 3, 17), 'Status': 'Scheduled'}, {
    'Task': 'SNP-337', 'y': 4, 'Start': datetime.date(2022, 5, 21),
    'Finish': datetime.date(2022, 5, 23), 'Status': 'Backlog'}, {
    'Task': 'SNP-352', 'y': 5, 'Start': datetime.date(2022, 2, 26),
    'Finish': datetime.date(2022, 2, 28), 'Status': 'Clarification'}, {
    'Task': 'SNP-239', 'y': 6, 'Start': datetime.date(2022, 5, 24),
    'Finish': datetime.date(2022, 5, 25), 'Status': 'Selected'}]
# fmt: on
df = pandas.DataFrame(task_list)

# put status into figure as well as customdata
fig = px.timeline(
    df,
    x_start="Start",
    x_end="Finish",
    y="y",
    # color="Status",
    hover_data=["Status"],
)

# build a colormap for status 
colormap = {s:c for s,c in zip(df["Status"].unique(), px.colors.qualitative.Plotly)}
# use status in customdata to map color
fig.update_traces(marker_color=[colormap[s[0]] for s in fig.data[0].customdata])

Answer 2

I've found the answer, but spent more when 2 hours and I found this accidentally.

# Format for your call/bar/trace
# Set/align bar HEIGHT to one. Prevent to make some of bar bigger or lower. 
fig.update_traces( width=0.6 )

Absolutely unpredictable place for these settings. I'm shocked.

Before

After

Full code:

import datetime
import pandas
import plotly.express as px

task_list = [{
    'Task': 'T-3', 'y': 0, 'Start': datetime.date(2022, 2, 24),
    'Finish': datetime.date(2022, 3, 17), 'Status': 'Scheduled'}, {
    'Task': 'SNP-350', 'y': 1, 'Start': datetime.date(2022, 2, 24),
    'Finish': datetime.date(2022, 2, 25), 'Status': 'Backlog'}, {
    'Task': 'RD-6687', 'y': 2, 'Start': datetime.date(2022, 3, 18),
    'Finish': datetime.date(2022, 4, 8), 'Status': 'Selected'}, {
    'Task': 'RD-6643', 'y': 3, 'Start': datetime.date(2022, 2, 24),
    'Finish': datetime.date(2022, 3, 17), 'Status': 'Scheduled'}, {
    'Task': 'SNP-337', 'y': 4, 'Start': datetime.date(2022, 5, 21),
    'Finish': datetime.date(2022, 5, 23), 'Status': 'Backlog'}, {
    'Task': 'SNP-352', 'y': 5, 'Start': datetime.date(2022, 2, 26),
    'Finish': datetime.date(2022, 2, 28), 'Status': 'Clarification'}, {
    'Task': 'SNP-239', 'y': 6, 'Start': datetime.date(2022, 5, 24),
    'Finish': datetime.date(2022, 5, 25), 'Status': 'Selected'}]

df = pandas.DataFrame(task_list)

fig = px.timeline(df, x_start="Start", x_end="Finish", y="y",
                   color="Status",
                  )
# Set/align bar HEIGHT to one. Prevent to make some of bar bigger or lower. 
fig.update_traces( width=0.6 )

fig.show()