René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"`_axes.py.scatter()` array index out of bound / calling from `seaborn`","articleBody":"### Bug report\r\n\r\n**Bug summary**\r\n\r\nSeeing this with `matplotlib 3.0.1` and `seaborn 0.9`. cc @mwaskom\r\n \r\n[matplotlib.axes._axes.scatter()](https://github.com/matplotlib/matplotlib/blob/921d4f4ab7ae2eb0feda02a364e8d63c6b6709c5/lib/matplotlib/axes/_axes.py#L4192) tests parameter `c` hits `array index out of bound` when `c` is an empty array. \r\n\r\nI encountered this while using `seaborn.swarmplot()` with `hue=` parameter. Essentially this plots each group (`hue`, in addition to x-axis category) and some times a group can be empty for a major x-axis category. \r\n\r\nSuggest potential fix to test length of `c` as well before accessing `c[0]`. \r\n\r\n```\r\n        if (c_none or\r\n                co is not None or\r\n                isinstance(c, str) or\r\n                (isinstance(c, collections.Iterable) and \r\n                    len(c) \u003e 0 and # proposed fix here\r\n                    isinstance(c[0], str))):\r\n```\r\n\r\n**Code for reproduction**\r\n\r\n\u003c!--A minimum code snippet required to reproduce the bug, also minimizing the number of dependencies required--\u003e\r\n\r\n```python\r\nimport pandas as pd\r\nimport seaborn as sns\r\n\r\ndf = pd.DataFrame(dict(category=['a', 'a', 'b', 'b', 'c'],\r\n                       hue=['x', 'y', 'x', 'y', 'x'],\r\n                       values=[1, 2, 3, 4, 3]))\r\nsns.swarmplot('category', 'values', hue='hue', data=df, dodge=True)\r\n```\r\n\r\n**Actual outcome**\r\n\r\nThis is the error I see:\r\n\r\n```\r\nIndexError                                Traceback (most recent call last)\r\n\u003cipython-input-5-0368a082f6a8\u003e in \u003cmodule\u003e\r\n----\u003e 1 sns.swarmplot('category', 'values', hue='hue', data=df, dodge=True)\r\n\r\nh:\\anaconda3\\lib\\site-packages\\seaborn\\categorical.py in swarmplot(x, y, hue, data, order, hue_order, dodge, orient, color, palette, size, edgecolor, linewidth, ax, **kwargs)\r\n   2989                        linewidth=linewidth))\r\n   2990 \r\n-\u003e 2991     plotter.plot(ax, kwargs)\r\n   2992     return ax\r\n   2993 \r\n\r\nh:\\anaconda3\\lib\\site-packages\\seaborn\\categorical.py in plot(self, ax, kws)\r\n   1444     def plot(self, ax, kws):\r\n   1445         \"\"\"Make the full plot.\"\"\"\r\n-\u003e 1446         self.draw_swarmplot(ax, kws)\r\n   1447         self.add_legend_data(ax)\r\n   1448         self.annotate_axes(ax)\r\n\r\nh:\\anaconda3\\lib\\site-packages\\seaborn\\categorical.py in draw_swarmplot(self, ax, kws)\r\n   1429                     kws.update(c=point_colors)\r\n   1430                     if self.orient == \"v\":\r\n-\u003e 1431                         points = ax.scatter(cat_pos, swarm_data, s=s, **kws)\r\n   1432                     else:\r\n   1433                         points = ax.scatter(swarm_data, cat_pos, s=s, **kws)\r\n\r\nh:\\anaconda3\\lib\\site-packages\\matplotlib\\__init__.py in inner(ax, data, *args, **kwargs)\r\n   1803                         \"the Matplotlib list!)\" % (label_namer, func.__name__),\r\n   1804                         RuntimeWarning, stacklevel=2)\r\n-\u003e 1805             return func(ax, *args, **kwargs)\r\n   1806 \r\n   1807         inner.__doc__ = _add_data_doc(inner.__doc__,\r\n\r\nh:\\anaconda3\\lib\\site-packages\\matplotlib\\axes\\_axes.py in scatter(self, x, y, s, c, marker, cmap, norm, vmin, vmax, alpha, linewidths, verts, edgecolors, **kwargs)\r\n   4194                 (isinstance(c, collections.Iterable) and\r\n   4195                     # len(c) \u003e 0 and\r\n-\u003e 4196                     isinstance(c[0], str))):\r\n   4197             c_array = None\r\n   4198         else:\r\n\r\nIndexError: index 0 is out of bounds for axis 0 with size 0\r\n```\r\n\r\nHappy to create a PR if we have happy with the proposed length test.\r\n","author":{"url":"https://github.com/esvhd","@type":"Person","name":"esvhd"},"datePublished":"2018-10-26T12:44:49.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":28},"url":"https://github.com/12641/matplotlib/issues/12641"}