Grouped plot legend does not create legend entry for first group

[michaelaye]

Bug shown at the end of this:
http://nbviewer.ipython.org/gist/michaelaye/4af80037146dfb65b105

Output of pd.show__versions():

INSTALLED VERSIONS

commit: None
python: 3.4.3.final.0
python-bits: 64
OS: Linux
OS-release: 2.6.32-431.11.2.el6.x86_64
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: None
LANG: en_US.UTF-8

pandas: 0.16.0-151-gcef3c85
nose: 1.3.6
Cython: 0.22
numpy: 1.9.2
scipy: 0.15.1
statsmodels: 0.6.1
IPython: 3.2.0-dev
sphinx: 1.2.3
patsy: 0.3.0
dateutil: 2.4.2
pytz: 2015.2
bottleneck: None
tables: 3.1.1
numexpr: 2.3.1
matplotlib: 1.4.3
openpyxl: None
xlrd: None
xlwt: None
xlsxwriter: None
lxml: None
bs4: None
html5lib: None
httplib2: None
apiclient: None
sqlalchemy: 0.9.9
pymysql: None
psycopg2: None

[sinhrks]

Blank legend looks to be caused by this line. legendHandles seems not to be guaranteed as public in mpl.
https://github.com/pydata/pandas/blob/master/pandas/tools/plotting.py#L1123

The result when I change the internal logic to use ax.get_legend_handles_labels:

Above shows unnecessary legend though...

[Jython1415]

Cannot reproduce this issue on v2.0.2. The following code snippit, copied and simplified from the link in the original report, runs without issue in a standard Python notebook.

import pandas as pd
import matplotlib.pyplot as plt
df = pd.DataFrame({'x': [2,3,2,3,2,3], 'XUV':[1,2,1,2,1,2]})
df.plot()
_, ax = plt.subplots()
ax = df.x.plot()
_, ax = plt.subplots()
ax = df.groupby('XUV').x.plot(style='*', ms=15, legend=True,ylim=(1,5))
_, ax = plt.subplots()
ax =  df.groupby('XUV').x.plot(style='*', ms=15, legend=True,ylim=(1,5))

I believe this issue can be closed.

Installed Versions

INSTALLED VERSIONS
------------------
commit           : 965ceca9fd796940050d6fc817707bba1c4f9bff
python           : 3.10.10.final.0
python-bits      : 64
OS               : Darwin
OS-release       : 22.5.0
Version          : Darwin Kernel Version 22.5.0: Mon Apr 24 20:52:43 PDT 2023; root:xnu-8796.121.2~5/RELEASE_ARM64_T8112
machine          : arm64
processor        : i386
byteorder        : little
LC_ALL           : None
LANG             : None
LOCALE           : None.UTF-8

pandas           : 2.0.2
numpy            : 1.24.3
pytz             : 2023.3
dateutil         : 2.8.2
setuptools       : 65.5.0
pip              : 23.1.2
Cython           : None
pytest           : None
hypothesis       : None
sphinx           : None
blosc            : None
feather          : None
xlsxwriter       : None
lxml.etree       : None
html5lib         : None
pymysql          : None
psycopg2         : None
jinja2           : None
IPython          : 8.14.0
pandas_datareader: None
bs4              : None
bottleneck       : None
brotli           : None
fastparquet      : None
fsspec           : None
gcsfs            : None
matplotlib       : 3.7.1
numba            : None
numexpr          : None
odfpy            : None
openpyxl         : None
pandas_gbq       : None
pyarrow          : None
pyreadstat       : None
pyxlsb           : None
s3fs             : None
scipy            : None
snappy           : None
sqlalchemy       : None
tables           : None
tabulate         : None
xarray           : None
xlrd             : None
zstandard        : None
tzdata           : 2023.3
qtpy             : None
pyqt5            : None