Missing marker when using style=...

[tamasgal]

There is an issue with the markers in the legend when working with the built-in matplotlib plot-wrapper in pandas. The problem is also in earlier versions and the only workaround I found is using matplotlib directly.

A small, complete example of the issue

import pandas as pd
import matplotlib.pyplot as plt

df = pd.DataFrame({'A': [1, 2, 3, 4, 5, 6],
                   'B': [2, 4, 1, 3, 2, 4],
                   'C': [3, 3, 2, 6, 4, 2],
                   'X': [1, 2, 3, 4, 5, 6]})

fig, ax = plt.subplots()

for kind in 'ABC':
    df.plot('X', kind, label=kind, ax=ax, style='.')

plt.show()

Expected Output

The markers in the legend are missing, except for the last label. It however works if I don't use style=..., but the default line-plot, like in this example:

import pandas as pd
import matplotlib.pyplot as plt

df = pd.DataFrame({'A': [1, 2, 3, 4, 5, 6],
                   'B': [2, 4, 1, 3, 2, 4],
                   'C': [3, 3, 2, 6, 4, 2],
                   'X': [1, 2, 3, 4, 5, 6]})

fig, ax = plt.subplots()

for kind in 'ABC':
    df.plot('X', kind, label=kind, ax=ax)

plt.show()

Output of pd.show_versions()

INSTALLED VERSIONS ------------------ commit: None python: 3.5.2.final.0 python-bits: 64 OS: Darwin OS-release: 16.1.0 machine: x86_64 processor: i386 byteorder: little LC_ALL: en_US.UTF-8 LANG: en_US.UTF-8 LOCALE: en_US.UTF-8

pandas: 0.19.0
nose: None
pip: 8.1.2
setuptools: 25.2.0
Cython: 0.24.1
numpy: 1.11.2
scipy: 0.18.1
statsmodels: None
xarray: None
IPython: 5.1.0
sphinx: None
patsy: None
dateutil: 2.5.3
pytz: 2016.7
blosc: None
bottleneck: None
tables: 3.3.0
numexpr: 2.6.1
matplotlib: 1.5.3
openpyxl: None
xlrd: None
xlwt: None
xlsxwriter: None
lxml: None
bs4: None
html5lib: None
httplib2: None
apiclient: None
sqlalchemy: None
pymysql: None
psycopg2: None
jinja2: 2.8
boto: None
pandas_datareader: None

[tamasgal]

I tracked down the problem to a single line in the sources.

This call is the final one, which sets the legends with the missing points except for the last ax when using style='.'
https://github.com/pandas-dev/pandas/blob/master/pandas/tools/plotting.py#L1293

If you change it from ax.legend(handles, labels, loc='best', title=title) to a plain ax.legend(), every marker is shown correctly in the legend. However, all optional settings are then of course skipped.

This line is the one which adds the legend handle in this case: https://github.com/pandas-dev/pandas/blob/master/pandas/tools/plotting.py#L1744

self._add_legend_handle(newlines[0], label, index=i)

However, I am still not able to figure out what is wrong there, the variable values look fine there too...

[charlesdong1991]

work on master, previously uploaded wrong pic, sorry

[tamasgal]

Thanks!