px.timeline loses type of x_end values

[eyak]

While px.timeline uses x_end values as expected and creates the proper graph,
trying to display the x_end values either as text or as hoverdata fails

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

data = pd.DataFrame([{
    'Start Date': datetime.datetime(2020, 1, 1),
    'End Date': datetime.datetime(2020, 2, 1),
    'Test Date': datetime.datetime(2020, 2, 1),
    'y': 100
},
    {
    'Start Date': datetime.datetime(2020, 1, 10),
    'End Date': datetime.datetime(2020, 2, 10),
    'Test Date': datetime.datetime(2020, 2, 10),
    'y': 90
}])

hover_data = {
    'Start Date': '|%x',
    'End Date': '|%x',
    'Test Date': '|%x'
}

fig = px.timeline(data, x_start="Start Date", x_end="End Date",
                  y="y", text='End Date', hover_data=hover_data)
fig.show()

[eyak]

Here's what happens inside process_dataframe_timeline:

plotly.py/packages/python/plotly/plotly/express/_core.py

Lines 1608 to 1609 in fe7a5d5

	# note that we are not adding any columns to the data frame here, so no risk of overwrite
	args["data_frame"][args["x_end"]] = (x_end - x_start).astype("timedelta64[ms]")

x_end is overwritten internally, so downstream references to x_end result in the 'massaged' data instead of the original data

[nicolaskruchten]

Related to/duplicate of #2518 ... it seems like at the moment, using text="End Date" or having "End Date" in hover_data causes type issues.

[nicolaskruchten]

See also https://community.plotly.com/t/issue-with-px-timeline-datetime-formats/43641/17

[nicolaskruchten]

OK, so I have a fix for the hover_data case, but I won't have a fix for the text case for a while, so I'm breaking that off into a separate issue here: #3019

For now, the workaround for text is to pass in a separate column:

import plotly.express as px
import pandas as pd

df = pd.DataFrame([
    dict(Task="Job A", Start='2009-01-01', Finish='2009-02-28', Resource="Alex"),
    dict(Task="Job B", Start='2009-03-05', Finish='2009-04-15', Resource="Alex"),
    dict(Task="Job C", Start='2009-02-20', Finish='2009-05-30', Resource="Max")
])
fig = px.timeline(df, x_start="Start", x_end="Finish", y="Task", text=df["Finish"].copy())
fig.update_yaxes(autorange="reversed")
fig.show()