DOC: updated the pandas.DataFrame.plot.hexbin docstring
Checklist for the pandas documentation sprint (ignore this if you are doing
an unrelated PR):

- [x] PR title is "DOC: update the <your-function-or-method> docstring"
- [x] The validation script passes: `scripts/validate_docstrings.py <your-function-or-method>`
- [x] The PEP8 style check passes: `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] The html version looks good: `python doc/make.py --single <your-function-or-method>`
- [x] It has been proofread on language by another sprint participant

Please include the output of the validation script below between the "```" ticks:

```

################################################################################
################### Docstring (pandas.DataFrame.plot.hexbin) ###################
################################################################################

Make hexagonal binning plots.

Make an hexagonal binning plot of *x* versus *y*, where *x*,
*y* are 1-D sequences of the same length, *N*. If *C* is *None*
(the default), this is an histogram of the number of occurrences
of the observations at (x[i],y[i]).

If *C* is specified, specifies values at given coordinates
(x[i],y[i]). These values are accumulated for each hexagonal
bin and then reduced according to *reduce_C_function*, having as default
the numpy's mean function (np.mean). (If *C* is
specified, it must also be a 1-D sequence of the same length
as *x* and *y*.)

Parameters
----------
x : label or position, optional
    Coordinates for x point.
y : label or position, optional
    Coordinates for y point.
C : label or position, optional
    The value at each `(x, y)` point.
reduce_C_function : callable, optional, default `mean`
    Function of one argument that reduces all the values in a bin to
    a single number (e.g. `mean`, `max`, `sum`, `std`).
gridsize : int, optional, 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.
kwds : optional
    Keyword arguments to pass on to :py:meth:`pandas.DataFrame.plot`.

Returns
-------
axes : matplotlib.AxesSubplot or np.array of them.

See Also
--------
matplotlib.pyplot.hexbin : hexagonal binning plot using matplotlib.

Examples
--------

.. plot::
    :context: close-figs

    >>> from  sklearn.datasets import load_iris
    >>> iris = load_iris()
    >>> df = pd.DataFrame(iris.data, columns=iris.feature_names)
    >>> hexbin = df.plot.hexbin(x='sepal length (cm)', y='sepal width (cm)',
    ...                         gridsize=10, cmap='viridis')

################################################################################
################################## Validation ##################################
################################################################################

Docstring for "pandas.DataFrame.plot.hexbin" correct. :)


```
thanks to @Renton2017
Hello @BielStela! Thanks for updating the PR.



Cheers ! There are no PEP8 issues in this Pull Request. :beers: 

##### Comment last updated on March 14, 2018 at 12:39 Hours UTC # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/20121?src=pr&el=h1) Report
> Merging [#20121](https://codecov.io/gh/pandas-dev/pandas/pull/20121?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/cad6dc7afb9e3a2571cba9112632a963cc63ade6?src=pr&el=desc) will **decrease** coverage by `0.07%`.
> The diff coverage is `n/a`.

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```diff
@@            Coverage Diff             @@
##           master   #20121      +/-   ##
==========================================
- Coverage   91.77%    91.7%   -0.08%     
==========================================
  Files         152      150       -2     
  Lines       49185    49152      -33     
==========================================
- Hits        45140    45074      -66     
- Misses       4045     4078      +33
```

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| [pandas/core/indexes/datetimelike.py](https://codecov.io/gh/pandas-dev/pandas/pull/20121/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9kYXRldGltZWxpa2UucHk=) | `96.7% <0%> (-0.02%)` | :arrow_down: |
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------

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 Probably callable

________________________________
From: BielStela <notifications@github.com>
Sent: Monday, March 12, 2018 5:24:47 PM
To: pandas-dev/pandas
Cc: Tom Augspurger; Comment
Subject: Re: [pandas-dev/pandas] DOC: updated the pandas.DataFrame.plot.hexbin docstring (#20121)


@BielStela commented on this pull request.

________________________________

In pandas/plotting/_core.py<https://github.com/pandas-dev/pandas/pull/20121#discussion_r173966391>:

>
         Parameters
         ----------
-        x, y : label or position, optional
-            Coordinates for each point.
+        x : label or position


Yes, I forgot about the type. I have a doubt with reduce_C_function parameter: it only accepts numpy functions in the form np.mean or np.std not strings like 'mean'. Is function (or func) the correct type reference?

—
You are receiving this because you commented.
Reply to this email directly, view it on GitHub<https://github.com/pandas-dev/pandas/pull/20121#discussion_r173966391>, or mute the thread<https://github.com/notifications/unsubscribe-auth/ABQHIlrmDmK0dzTrM7Rx4i92_bWqx6GOks5tdvWvgaJpZM4SlQ_G>.
 Fixed the PEP8 issue and conflict with master 1 sec. Fixing some grammar.

It's *a* hexagonal :) @BielStela I made a small edit in the actual plot. The default gridsize seems rather useless, so I added one to the first plot to make it look a bit better. I also removed the cmap there (because the "inferno" has dark low values, it is not really fitting for a hexbin IMO, but added a custom cmap to the second example) @jorisvandenbossche you want to fixup @datapythonista's points? OK, editing via github at the same time is not a good idea :-) 
@TomAugspurger I will add your changes back, and do the ones of @datapythonista  @BielStela Thanks a lot for the PR! :)

FYI Joris, https://github.com/github/hub is nice for checking out PRs. Just
`hub checkout <url>` and all the remotes are setup locally.

On Wed, Mar 14, 2018 at 7:41 AM, Joris Van den Bossche <
notifications@github.com> wrote:

> @BielStela <https://github.com/bielstela> Thanks a lot for the PR!
>
> —
> You are receiving this because you were mentioned.
> Reply to this email directly, view it on GitHub
> <https://github.com/pandas-dev/pandas/pull/20121#issuecomment-373006788>,
> or mute the thread
> <https://github.com/notifications/unsubscribe-auth/ABQHImg9KQ2qzkpCkVzHn4Rpgm8AdP2Iks5teQ_ngaJpZM4SlQ_G>
> .
>
 Also, welcome to take a look in a few hours how the pages is looking to check everything is OK: http://pandas-docs.github.io/pandas-docs-travis/generated/pandas.DataFrame.plot.hexbin.html#pandas.DataFrame.plot.hexbin @TomAugspurger I have my alias `git pr <number>` which basically does the same I suppose (and normally I do that to test PRs, but for the doc prs now I was mainly using the github edit interface for really minor things) Thanks a lot for the help and for the hard work you do!