“ValueError: num must be 1 <= num <= 0, not 1” trying to plot a histogram for a Pandas DataFrame?

“ValueError: num must be 1 <= num <= 0, not 1” trying to plot a histogram for a Pandas DataFrame?

I have a&nbsp;pandas.DataFrame&nbsp;of which one of the columns,&nbsp;'Time', contains&nbsp;datetime&nbsp;objects:

I have a pandas.DataFrame of which one of the columns, 'Time', contains datetime objects:

In [3]: df['Time']                                                                                             
Out[3]: 
req_id
d95bc740-d320-4d80-b851-81b7b7758a8f   2019-01-17 23:29:43.043
0df512ee-094c-46ce-a041-a6a9c90fddef   2019-01-17 23:26:29.464
e87807b3-b681-4343-8ba3-9e35df99f2d5   2019-01-17 23:17:34.659
cc638d8a-947d-40ec-8488-9292f801eb5b   2019-01-17 23:15:26.953
b710d0e8-7e51-49c1-9bda-6abca2794fa8   2019-01-17 23:15:05.375
142fbb7a-6472-4d4e-a5b9-5a4a4d4ae747   2019-01-17 23:14:51.050
6a0dd117-6d1e-4a2e-9efa-f2cac73b1aa0   2019-01-17 23:14:26.762
03ed901e-f6fb-47b3-bcea-d4afa7432bd3   2019-01-17 23:12:10.766
1b6c8326-518e-4c62-8a72-84052cd6f024   2019-01-17 23:11:30.688
d4f3144a-56d8-438d-bc0d-4e8d0afee2ff   2019-01-17 23:10:10.456
43976955-f32c-494b-b7f4-5c04abc2108a   2019-01-17 23:10:07.456
1f8a88d2-e4fd-437f-852f-026ed0eb30e7   2019-01-17 23:09:48.396
7fc550a1-2df1-4839-b5fd-59cf1d6c9c0e   2019-01-17 23:09:28.372
2cd8481e-79ab-4491-bcac-18761b9381ce   2019-01-17 23:09:08.752
18b2dc35-fae6-4e75-abd2-5bdadd8a1079   2019-01-17 23:08:14.430
43cc41f4-18cf-4854-8c78-89805f902dbf   2019-01-17 23:05:32.962
f27e1c06-4f69-4a76-bb80-49799b897edb   2019-01-17 23:04:33.882
c641e2d1-4560-406f-a5b0-46e9bd27207d   2019-01-17 23:03:43.959
f3726c23-d3ae-4a87-94b0-6462f9de733c   2019-01-17 23:03:27.322
e0fb0974-fc1f-48b6-a7b5-b647e0d33fd2   2019-01-17 23:03:06.342
c968bbd4-6e44-4920-a4a3-d5b7632f232d   2019-01-17 23:03:01.342
41b811f8-98ca-4cd3-97b8-ab9c6287ab98   2019-01-17 23:00:47.052
ca6d86cd-7293-41c2-a976-c70403dca18e   2019-01-17 22:58:58.446
97a83d4d-a847-4953-b411-49847b821683   2019-01-17 22:58:50.723
05ccb053-a56a-42bd-acec-08fddc71c26b   2019-01-17 22:58:03.835
b5af2bbb-9121-4d5f-bf30-6310c5b88584   2019-01-17 22:57:01.791
839541a4-5ae6-4081-bff0-c3799beda90f   2019-01-17 22:56:40.152
cc9e46e3-d437-4d19-a4fe-3245f5e840be   2019-01-17 22:56:27.432
672d1115-10e0-40b8-9ca7-40b0d587c85a   2019-01-17 22:56:09.961
7eb5afd7-dc48-4bb2-bb51-cf33dfeafe3f   2019-01-17 22:52:42.589
                                                 ...          
eb2bb272-2205-43b2-8984-927cfffbc2fd   2019-01-14 12:45:35.045
8bcee5a8-2244-4f1f-bbf4-f05cd40513ed   2019-01-14 12:38:43.214
b0d312fb-01d2-4398-bf3f-798aab7f914d   2019-01-14 12:38:14.694
d7ce9ed6-db9d-4c0c-8256-7d94e135341f   2019-01-14 12:11:20.465
cfbda676-331c-4cb8-afbb-ad195a035d13   2019-01-14 12:10:21.011
3fd28c37-44d3-4031-8507-a15b1bbbb1d1   2019-01-14 11:41:04.615
9fd55a9d-33ff-47cd-888b-01bc0b5e1793   2019-01-14 10:50:34.951
bc84a61f-a368-4119-9522-6c6bd5fd4408   2019-01-14 10:38:12.292
6a69d9e8-2a49-4762-abd1-c6ce79f48986   2019-01-14 10:31:24.628
ab043246-5ea3-41ec-9a7b-1db7b7b6c863   2019-01-14 09:29:04.368
6bbe661f-da05-4811-b719-d7a14ba262e5   2019-01-14 06:55:29.992
e5c4bfa3-a052-4c8c-929b-8f5000a24acd   2019-01-14 06:51:05.613
9a116376-5340-42f4-9bce-6d9d05ea7bee   2019-01-14 06:42:46.614
5b971ccf-0f55-4244-a433-49e590e7d5de   2019-01-14 06:37:49.787
fd10da87-2187-4804-9e4d-a6a7d1cef375   2019-01-14 06:24:42.298
b9faaa07-ec43-4add-b0f7-b5a40968d573   2019-01-14 04:32:17.795
688b367b-e9f7-413d-9e60-4e1b73a138f2   2019-01-14 04:06:16.833
fcf902c7-dba9-4b51-89bb-36668ec447d2   2019-01-14 02:50:02.308
bedfd669-5f2f-44c2-b26c-32a3835196c8   2019-01-14 02:48:28.684
ea3c6ed4-f98b-4032-8cf8-df78bf04c4f7   2019-01-14 02:47:13.542
1817d944-e71a-4f74-95b8-6ceb5e529ca8   2019-01-14 02:46:02.994
732c0c33-5824-4876-a530-fce7911e47fe   2019-01-14 02:44:04.990
f54efa6c-2379-4d3d-a8ec-6388db46b8b7   2019-01-14 02:42:27.867
c348cc27-4906-4fd0-980f-fc96dcf0115f   2019-01-14 02:40:45.497
5d11ae5c-1d7a-41e8-9963-dd051f091ad9   2019-01-14 02:39:25.439
f692de03-389e-4ca8-bc19-fc13bff379df   2019-01-14 02:38:06.084
44f79ab5-aca4-480a-b5f7-24df5ea887ba   2019-01-14 02:36:24.071
98f64b91-6192-4ae3-8d26-d65e50835a26   2019-01-14 02:15:56.977
b581804c-ef22-4b18-90a4-a4df260c91c5   2019-01-14 02:06:31.885
93f57887-7840-4b08-be9e-7e239f6eb569   2019-01-14 02:03:37.644
Name: Time, Length: 367, dtype: datetime64[ns]

I'd like to plot a histogram of these times. However if I try

df.hist(column='Time')

I get the following error message:

---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-2-6b19a0524017> in <module>
----> 1 exec(open('analysis/check_refunds_fix.py').read())

<string> in <module>

/usr/local/lib/python3.7/site-packages/pandas/plotting/_core.py in hist_frame(data, column, by, grid, xlabelsize, xrot, ylabelsize, yrot, ax, sharex, sharey, figsize, layout, bins, **kwds) 2406 fig, axes = _subplots(naxes=naxes, ax=ax, squeeze=False, 2407 sharex=sharex, sharey=sharey, figsize=figsize, -> 2408 layout=layout) 2409 _axes = _flatten(axes) 2410

/usr/local/lib/python3.7/site-packages/pandas/plotting/_tools.py in _subplots(naxes, sharex, sharey, squeeze, subplot_kw, ax, layout, layout_type, *fig_kw) 236 237 # Create first subplot separately, so we can share it if requested --> 238 ax0 = fig.add_subplot(nrows, ncols, 1, *subplot_kw) 239 240 if sharex:

/usr/local/lib/python3.7/site-packages/matplotlib/figure.py in add_subplot(self, args, *kwargs) 1365 self._axstack.remove(ax) 1366 -> 1367 a = subplot_class_factory(projection_class)(self, args, *kwargs) 1368 self._axstack.add(key, a) 1369 self.sca(a)

/usr/local/lib/python3.7/site-packages/matplotlib/axes/subplots.py in _init(self, fig, args, *kwargs) 58 raise ValueError( 59 ("num must be 1 <= num <= {maxn}, not {num}" ---> 60 ).format(maxn=rows*cols, num=num)) 61 self._subplotspec = GridSpec( 62 rows, cols, figure=self.figure)[int(num) - 1]

ValueError: num must be 1 <= num <= 0, not 1

The error message doesn't really make sense to me, because no number num can satisfy 1 <= num <= 0. I've tried to reproduce this with a 'simple' example but there I do get a histogram. Any ideas what the issue might be here?

Update

I've set a trace in the matplotlib source code for the SubplotBase class:

class SubplotBase(object):
    """
    Base class for subplots, which are :class:Axes instances with
    additional methods to facilitate generating and manipulating a set
    of :class:Axes within a figure.
    """

def __init__(self, fig, *args, **kwargs):
    """
    *fig* is a :class:`matplotlib.figure.Figure` instance.

    *args* is the tuple (*numRows*, *numCols*, *plotNum*), where
    the array of subplots in the figure has dimensions *numRows*,
    *numCols*, and where *plotNum* is the number of the subplot
    being created.  *plotNum* starts at 1 in the upper left
    corner and increases to the right.

    If *numRows* &lt;= *numCols* &lt;= *plotNum* &lt; 10, *args* can be the
    decimal integer *numRows* * 100 + *numCols* * 10 + *plotNum*.
    """

    self.figure = fig

    if len(args) == 1:
        if isinstance(args[0], SubplotSpec):
            self._subplotspec = args[0]
        else:
            try:
                s = str(int(args[0]))
                rows, cols, num = map(int, s)
            except ValueError:
                raise ValueError('Single argument to subplot must be '
                    'a 3-digit integer')
            self._subplotspec = GridSpec(rows, cols,
                                         figure=self.figure)[num - 1]
            # num - 1 for converting from MATLAB to python indexing
    elif len(args) == 3:
        rows, cols, num = args
        rows = int(rows)
        cols = int(cols)
        if isinstance(num, tuple) and len(num) == 2:
            num = [int(n) for n in num]
            self._subplotspec = GridSpec(
                    rows, cols,
                    figure=self.figure)[(num[0] - 1):num[1]]
        else:
            if num &lt; 1 or num &gt; rows*cols:
                raise ValueError(
                    ("num must be 1 &lt;= num &lt;= {maxn}, not {num}"
                    ).format(maxn=rows*cols, num=num))
            self._subplotspec = GridSpec(
                    rows, cols, figure=self.figure)[int(num) - 1]
            # num - 1 for converting from MATLAB to python indexing
    else:
        raise ValueError('Illegal argument(s) to subplot: %s' % (args,))

In the elif len(args) == 3 block, I can confirm that the constructor was called with rows = 1, cols = 0, and num = 1. I guess the problem is that cols = 0; why is it trying to initialize a subplot without any columns?

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