BUG: DataFrame html repr does not work for complex dtypes if DataFrame is empty

[jasonboh]

Pandas version checks

• I have checked that this issue has not already been reported.

• I have confirmed this bug exists on the latest version of pandas.

• I have confirmed this bug exists on the main branch of pandas.

Reproducible Example

# %%
dfe1 = pd.DataFrame({"x": np.array([], dtype="complex")})
dfe1
# %%
dfe2 = pd.DataFrame({"x": np.array([], dtype="float")})
dfe2

Issue Description

The above example must be run in a Jupyter notebook so that the html repr method gets called. For the dfe1 empty DataFrame, the error is ValueError: max() arg is an empty sequence. For dfe2, everything works correctly and the html repr is shown.

Expected Behavior

dfe1 repr shoudl be same as dfe2 repr in a Jupyter notebook.

Installed Versions

INSTALLED VERSIONS

commit : 0f43794
python : 3.10.4.final.0
python-bits : 64
OS : Windows
OS-release : 10
Version : 10.0.19044
machine : AMD64
processor : Intel64 Family 6 Model 141 Stepping 1, GenuineIntel
byteorder : little
LC_ALL : None
LANG : None
LOCALE : English_United States.1252

pandas : 2.0.3
numpy : 1.24.3
pytz : 2022.7.1
dateutil : 2.8.2
setuptools : 58.1.0
pip : 22.0.4
Cython : 0.29.33
pytest : 7.2.1
hypothesis : None
sphinx : 5.3.0
blosc : None
feather : None
xlsxwriter : None
lxml.etree : None
html5lib : None
pymysql : None
psycopg2 : None
jinja2 : 3.1.2
IPython : 8.10.0
pandas_datareader: None
bs4 : None
bottleneck : None
brotli : None
fastparquet : None
fsspec : 2023.6.0
gcsfs : None
matplotlib : 3.7.0
numba : None
numexpr : None
odfpy : None
openpyxl : 3.1.2
pandas_gbq : None
pyarrow : 12.0.1
pyreadstat : None
pyxlsb : None
s3fs : None
scipy : 1.10.1
snappy : None
sqlalchemy : None
tables : None
tabulate : None
xarray : None
xlrd : None
zstandard : None
tzdata : 2023.3
qtpy : None
pyqt5 : None

[lithomas1]

Thanks, I can also reproduce this on main

For reference the traceback is

>>> dfe1.to_html()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/thomasli/pandas/pandas/core/frame.py", line 3162, in to_html
    return fmt.DataFrameRenderer(formatter).to_html(
  File "/Users/thomasli/pandas/pandas/io/formats/format.py", line 1074, in to_html
    string = html_formatter.to_string()
  File "/Users/thomasli/pandas/pandas/io/formats/html.py", line 82, in to_string
    lines = self.render()
  File "/Users/thomasli/pandas/pandas/io/formats/html.py", line 88, in render
    self._write_table()
  File "/Users/thomasli/pandas/pandas/io/formats/html.py", line 263, in _write_table
    self._write_body(indent + self.indent_delta)
  File "/Users/thomasli/pandas/pandas/io/formats/html.py", line 411, in _write_body
    fmt_values = self._get_formatted_values()
  File "/Users/thomasli/pandas/pandas/io/formats/html.py", line 406, in _get_formatted_values
    fmt_values = {i: self.fmt.format_col(i) for i in range(self.ncols)}
  File "/Users/thomasli/pandas/pandas/io/formats/html.py", line 406, in <dictcomp>
    fmt_values = {i: self.fmt.format_col(i) for i in range(self.ncols)}
  File "/Users/thomasli/pandas/pandas/io/formats/format.py", line 893, in format_col
    return format_array(
  File "/Users/thomasli/pandas/pandas/io/formats/format.py", line 1298, in format_array
    return fmt_obj.get_result()
  File "/Users/thomasli/pandas/pandas/io/formats/format.py", line 1331, in get_result
    fmt_values = self._format_strings()
  File "/Users/thomasli/pandas/pandas/io/formats/format.py", line 1611, in _format_strings
    return list(self.get_result_as_array())
  File "/Users/thomasli/pandas/pandas/io/formats/format.py", line 1578, in get_result_as_array
    formatted_values = format_values_with(float_format)
  File "/Users/thomasli/pandas/pandas/io/formats/format.py", line 1556, in format_values_with
    result = _trim_zeros_complex(values, self.decimal)
  File "/Users/thomasli/pandas/pandas/io/formats/format.py", line 1965, in _trim_zeros_complex
    padded_length = max(len(part) for part in padded_parts) - 1
ValueError: max() arg is an empty sequence

It should be a pretty easy fix if you or someone else wants to put up a PR.
(Since the length of the array is zero, the value of padded_length doesn't really matter, so you just need to get it to not error. It would probably be reasonable to set it to 0 in the empty case though).

[harikirank]

take

[attack68]

Do you know how styler handles this:
df.style
Maybe that also needs fixing?

[harikirank]

Hi @attack68, I don't know how that works. Could you please help me?

[soumya1729]

hi @harikirank have you put in a PR for this yet?

[harikirank]

Hi @soumya1729, Not yet. If you want to work on this issue please go ahead.

[soumya1729]

@harikirank thanks, yeah would like to try!

[attack68]

You dont need to fix the Styler, just DataFrame.to_html, btw, this already works.