IndexError in repr of series objects containing complex numbers with negative imaginary parts

[DRMacIver]

Code Sample, a copy-pastable example if possible

from pandas import Series

print(Series([-1j]))

Problem description

This raises the following error:

Traceback (most recent call last):
  File "foo.py", line 3, in <module>
    print(Series([-1j]))
  File "/home/david/.pyenv/versions/3.7.4/lib/python3.7/site-packages/pandas/core/series.py", line 1611, in __repr__
    length=show_dimensions,
  File "/home/david/.pyenv/versions/3.7.4/lib/python3.7/site-packages/pandas/core/series.py", line 1677, in to_string
    result = formatter.to_string()
  File "/home/david/.pyenv/versions/3.7.4/lib/python3.7/site-packages/pandas/io/formats/format.py", line 312, in to_string
    fmt_values = self._get_formatted_values()
  File "/home/david/.pyenv/versions/3.7.4/lib/python3.7/site-packages/pandas/io/formats/format.py", line 299, in _get_formatted_values
    values_to_format, None, float_format=self.float_format, na_rep=self.na_rep
  File "/home/david/.pyenv/versions/3.7.4/lib/python3.7/site-packages/pandas/io/formats/format.py", line 1032, in format_array
    return fmt_obj.get_result()
  File "/home/david/.pyenv/versions/3.7.4/lib/python3.7/site-packages/pandas/io/formats/format.py", line 1063, in get_result
    fmt_values = self._format_strings()
  File "/home/david/.pyenv/versions/3.7.4/lib/python3.7/site-packages/pandas/io/formats/format.py", line 1288, in _format_strings
    return list(self.get_result_as_array())
  File "/home/david/.pyenv/versions/3.7.4/lib/python3.7/site-packages/pandas/io/formats/format.py", line 1252, in get_result_as_array
    formatted_values = format_values_with(float_format)
  File "/home/david/.pyenv/versions/3.7.4/lib/python3.7/site-packages/pandas/io/formats/format.py", line 1234, in format_values_with
    return _trim_zeros_complex(values, na_rep)
  File "/home/david/.pyenv/versions/3.7.4/lib/python3.7/site-packages/pandas/io/formats/format.py", line 1597, in _trim_zeros_complex
    return ["".join(separate_and_trim(x, na_rep)) for x in str_complexes]
  File "/home/david/.pyenv/versions/3.7.4/lib/python3.7/site-packages/pandas/io/formats/format.py", line 1597, in <listcomp>
    return ["".join(separate_and_trim(x, na_rep)) for x in str_complexes]
  File "/home/david/.pyenv/versions/3.7.4/lib/python3.7/site-packages/pandas/io/formats/format.py", line 1594, in separate_and_trim
    + ["j"]
IndexError: list index out of range

Expected Output

This should print something like the following:

0    0.0-1.0j
dtype: complex128

Output of pd.show_versions()

[paste the output of pd.show_versions() here below this line]

INSTALLED VERSIONS

commit : None
python : 3.7.4.final.0
python-bits : 64
OS : Linux
OS-release : 4.4.0-17134-Microsoft
machine : x86_64
processor : x86_64
byteorder : little
LC_ALL : None
LANG : en_US.UTF-8
LOCALE : en_US.UTF-8

pandas : 0.25.0
numpy : 1.16.4
pytz : 2019.1
dateutil : 2.8.0
pip : 19.0.3
setuptools : 40.8.0
Cython : None
pytest : 5.0.1
hypothesis : None
sphinx : None
blosc : None
feather : None
xlsxwriter : None
lxml.etree : None
html5lib : None
pymysql : None
psycopg2 : None
jinja2 : None
IPython : 7.6.1
pandas_datareader: None
bs4 : None
bottleneck : None
fastparquet : None
gcsfs : None
lxml.etree : None
matplotlib : None
numexpr : None
odfpy : None
openpyxl : None
pandas_gbq : None
pyarrow : None
pytables : None
s3fs : None
scipy : None
sqlalchemy : None
tables : None
xarray : None
xlrd : None
xlwt : None
xlsxwriter : None

[mroeschke]

PR #25745 is probably the culprit for this regression. Investigation and PR's welcome!