DOC: Hexbin creates inconsistent size of hexagons for nearly the same data, depending on distance from axis limits

[stelios-c]

• 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 master branch of pandas.

Reproducible Example

import pandas as pd
from io import StringIO
csv_data = "x,y\n1,1\n1,2\n2,1\n1,9\n9,1"
csv_data2 = "x,y\n1,1\n1,2\n2,1\n1,3\n3,1"
pd.read_csv(StringIO(csv_data)).plot(kind='hexbin',x='x',y='y',\
                   xlim=[-0.5,10.5],ylim=[0,10.5],\
                   gridsize=[10,10],sharex=False)
pd.read_csv(StringIO(csv_data2)).plot(kind='hexbin',x='x',y='y',\
                   xlim=[-0.5,10.5],ylim=[0,10.5],\
                   gridsize=[10,10],sharex=False)

Issue Description

csv_data gets plotted with big hexagons touching each other as expected. csv_data2 gets plotted with much smaller hexagons, probably because there is no data near the right xlim, upper ylim.

Expected Behavior

I was expecting the same size of hexagon for those two datasets

Installed Versions

INSTALLED VERSIONS

commit : 945c9ed
python : 3.7.10.final.0
python-bits : 64
OS : Linux
OS-release : 4.19.0-18-cloud-amd64
Version : #1 SMP Debian 4.19.208-1 (2021-09-29)
machine : x86_64
processor :
byteorder : little
LC_ALL : None
LANG : C.UTF-8
LOCALE : en_US.UTF-8

pandas : 1.3.4
numpy : 1.19.5
pytz : 2021.3
dateutil : 2.8.2
pip : 21.3
setuptools : 58.2.0
Cython : None
pytest : None
hypothesis : None
sphinx : None
blosc : None
feather : None
xlsxwriter : None
lxml.etree : None
html5lib : None
pymysql : None
psycopg2 : None
jinja2 : 3.0.2
IPython : 7.28.0
pandas_datareader: None
bs4 : None
bottleneck : 1.3.2
fsspec : 2021.10.1
fastparquet : None
gcsfs : 2021.10.1
matplotlib : 3.4.3
numexpr : None
odfpy : None
openpyxl : None
pandas_gbq : None
pyarrow : 5.0.0
pyxlsb : None
s3fs : None
scipy : 1.7.1
sqlalchemy : 1.4.26
tables : None
tabulate : None
xarray : None
xlrd : None
xlwt : None
numba : 0.54.1

[stelios-c]

[Lstsk]

Hello, I don't think this is a bug. The hexagon is getting small because it would have to adjust its size to fit data that is so close to each other. Perhaps, you could adjust the grid-size, xlim, and ylim to make the graph look better?

[stelios-c]

Thanks @Copastr . I'm trying to do an A/B type comparison so I want xlim and ylim to be the same. But I agree, it looks like grid size needs to be adjusted to the range of the data. Maybe this should be treated as a documentation bug because https://pandas.pydata.org/docs/reference/api/pandas.DataFrame.plot.hexbin.html only says

gridsizeint or tuple of (int, int), default 100
The number of hexagons in the x-direction. The corresponding number of hexagons in the y-direction is chosen in a way that the hexagons are approximately regular. Alternatively, gridsize can be a tuple with two elements specifying the number of hexagons in the x-direction and the y-direction.

This does not clarify that the hexagons are not all the way to xlim/ylim but only to the extent covered by the data.