Histogram doesn't accept bins="auto"

[stsievert]

All software version info

• hvplot 0.5.2, holoviews 1.13.2
• Pandas 1.0.2
• Numpy 1.18.1

Description of expected behavior and the observed behavior

NumPy's histogram function accepts the keyword argument bins="auto". I would expect the same from Holoviews (especially because it looks like Holoviews relies on np.histogram).

However, Holoviews throws an error when df.plot(..., kind="hist", bins="auto") is called.

Complete, minimal, self-contained example code that reproduces the issue

import pandas as pd
import hvplot.pandas
import numpy as np
df = pd.DataFrame({"x": np.random.uniform(size=200)})
df["x"].hvplot(kind="hist", bins=40)  # works
df["x"].hvplot(kind="hist", bins="auto")  # throws the error

Stack traceback and/or browser JavaScript console output

Here's the error:

~/anaconda3/lib/python3.7/site-packages/numpy/lib/histograms.py in _get_bin_edges(a, bins, range, weights)
    423         except TypeError:
    424             raise TypeError(
--> 425                 '`bins` must be an integer, a string, or an array')
    426         if n_equal_bins < 1:
    427             raise ValueError('`bins` must be positive, when an integer')

TypeError: `bins` must be an integer, a string, or an array

Here's the complete traceback:

---------------------------------------------------------------------
TypeError                           Traceback (most recent call last)
~/anaconda3/lib/python3.7/site-packages/numpy/lib/histograms.py in _get_bin_edges(a, bins, range, weights)
    421         try:
--> 422             n_equal_bins = operator.index(bins)
    423         except TypeError:

TypeError: only integer scalar arrays can be converted to a scalar index

During handling of the above exception, another exception occurred:

TypeError                           Traceback (most recent call last)
<ipython-input-51-108281d3bae9> in <module>
----> 1 df["x"].hvplot(kind="hist", bins="auto")  # fails

~/anaconda3/lib/python3.7/site-packages/hvplot/plotting/core.py in __call__(self, x, y, kind, **kwds)
     70                 return pn.panel(plot, **panel_dict)
     71 
---> 72         return self._get_converter(x, y, kind, **kwds)(kind, x, y)
     73 
     74     def _get_converter(self, x=None, y=None, kind=None, **kwds):

~/anaconda3/lib/python3.7/site-packages/hvplot/converter.py in __call__(self, kind, x, y)
    942                 obj = DynamicMap(cbcallable, streams=[self.stream])
    943             else:
--> 944                 obj = method(x, y)
    945 
    946         if self.crs and self.project:

~/anaconda3/lib/python3.7/site-packages/hvplot/converter.py in hist(self, x, y, data)
   1388                 hists = hists.layout() if self.subplots else hists.overlay()
   1389             else:
-> 1390                 hists = histogram(ds, dimension=y, **hist_opts)
   1391 
   1392             return hists.opts(opts).redim(**self._redim)

~/anaconda3/lib/python3.7/site-packages/param/parameterized.py in __new__(class_, *args, **params)
   2810         inst = class_.instance()
   2811         inst.param._set_name(class_.__name__)
-> 2812         return inst.__call__(*args,**params)
   2813 
   2814     def __call__(self,*args,**kw):

~/anaconda3/lib/python3.7/site-packages/holoviews/core/operation.py in __call__(self, element, **kwargs)
    194             kwargs['streams'] = self.p.streams
    195         kwargs['per_element'] = self._per_element
--> 196         return element.apply(self, **kwargs)
    197 
    198 

~/anaconda3/lib/python3.7/site-packages/holoviews/core/accessors.py in pipelined_call(*args, **kwargs)
     43 
     44             try:
---> 45                 result = __call__(*args, **kwargs)
     46 
     47                 if not in_method:

~/anaconda3/lib/python3.7/site-packages/holoviews/core/accessors.py in __call__(self, apply_function, streams, link_inputs, dynamic, per_element, **kwargs)
    196             if hasattr(apply_function, 'dynamic'):
    197                 inner_kwargs['dynamic'] = False
--> 198             return apply_function(self._obj, **inner_kwargs)
    199         elif self._obj._deep_indexable:
    200             mapped = []

~/anaconda3/lib/python3.7/site-packages/holoviews/core/operation.py in __call__(self, element, **kwargs)
    190             elif ((self._per_element and isinstance(element, Element)) or
    191                   (not self._per_element and isinstance(element, ViewableElement))):
--> 192                 return self._apply(element)
    193         elif 'streams' not in kwargs:
    194             kwargs['streams'] = self.p.streams

~/anaconda3/lib/python3.7/site-packages/holoviews/core/operation.py in _apply(self, element, key)
    130         element_pipeline = getattr(element, '_pipeline', None)
    131 
--> 132         ret = self._process(element, key)
    133         for hook in self._postprocess_hooks:
    134             ret = hook(self, ret, **kwargs)

~/anaconda3/lib/python3.7/site-packages/holoviews/operation/element.py in _process(self, element, key)
    753                     hist /= hist.max()
    754             else:
--> 755                 hist, edges = histogram(data, normed=normed, weights=weights, bins=edges)
    756                 if self.p.weight_dimension and self.p.mean_weighted:
    757                     hist_mean, _ = histogram(data, density=False, bins=self.p.num_bins)

<__array_function__ internals> in histogram(*args, **kwargs)

~/anaconda3/lib/python3.7/site-packages/numpy/lib/histograms.py in histogram(a, bins, range, normed, weights, density)
    793     a, weights = _ravel_and_check_weights(a, weights)
    794 
--> 795     bin_edges, uniform_bins = _get_bin_edges(a, bins, range, weights)
    796 
    797     # Histogram is an integer or a float array depending on the weights.

~/anaconda3/lib/python3.7/site-packages/numpy/lib/histograms.py in _get_bin_edges(a, bins, range, weights)
    423         except TypeError:
    424             raise TypeError(
--> 425                 '`bins` must be an integer, a string, or an array')
    426         if n_equal_bins < 1:
    427             raise ValueError('`bins` must be positive, when an integer')

TypeError: `bins` must be an integer, a string, or an array