Formatting Datetime Index with Pandas DataFrame Styler, to only show time-part

Question

I'm using the style property of Pandas DataFrames to create HTML tables for emailing.

The issue I am having is that I have a datetime index that shows up as a datetime stamp when I'd like it to show as a date instead. I'm not interested in the time part. In the interpreter, the DataFrame does print out correctly (only shows the date part). But when I render after stylizing using the style property of the table, it generates HTML that puts out the time part as well. I've looked into using style.format() but I can't access the index column. I would reset the index in order to make the datetime column a normal column... but my header columns are MultIndex. If I flatten out and don't use indexes the table looks weird.

Unfortunately I found this in the .style documentation:

Limitations

• DataFrame only (use Series.to_frame().style)
• The index and columns must be unique
• No large repr, and performance isn’t great; this is intended for summary DataFrames
• You can only style the values, not the index or columns
• You can only apply styles, you can’t insert new HTML entities Some of these will be addressed in the future.

https://pandas.pydata.org/pandas-docs/stable/style.html#Limitations

I'm posting to see if anyone has any ideas for how I can get around this. Thanks!

Example table that shows the issue: example_table_link

Code for generating table:

account_day_df = merged[['Day', 'Metric1', 'Metric2', 'Metric3', 'Metric4', 'Campaign type']]
account_day_df = account_day_df.groupby(['Day', 'Campaign type']).sum()
account_day_df.loc[:, 'Metric5'] = account_day_df['Metric1'] / account_day_df['Metric4']
account_day_df = account_day_df.unstack('Campaign type')

html += (
    account_day_df.style
        .background_gradient(cmap=cm, subset=['Metric5'])
        .set_table_attributes('border="1" class="dataframe table table-hover table-bordered"')
        .render(i)
)

Answer 1

As part of the Styler enhancements in pandas 1.4.0 format_index can now be used to style the index directly:

For Example:

df.style.format_index(lambda s: s.strftime("%Y-%m-%d"))

This can, of course, be chained with other styles:

(
    df.style.format_index(lambda s: s.strftime("%Y-%m-%d"))
        .format(precision=2)
        .background_gradient()
)

---

Setup:

import pandas as pd
from numpy.random import Generator, MT19937

rng = Generator(MT19937(10))
df = pd.DataFrame(
    rng.random(size=(10, 2)),
    index=pd.date_range('2022-01-01', periods=10, freq='D')
)

df.style