René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"scatter could not raise when colors are provided but position data are empty","articleBody":"The 3.0.x series added new checks in `scatter` for equivalence between the length of the `x`, `y` vectors and the length of the `c` vectors.\r\n\r\nThese changes have broken code in seaborn that sometimes calls scatter with empty position data but non-empty color data, e.g.\r\n\r\n```python\r\nimport matplotlib.pyplot as plt\r\nf, ax = plt.subplots()\r\nax.scatter([], [], c=[\"r\", \"b\", \"g\"])\r\n```\r\n```python-traceback\r\n---------------------------------------------------------------------------\r\nValueError                                Traceback (most recent call last)\r\n~/anaconda/envs/seaborn-dev/lib/python3.6/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   4237                     valid_shape = False\r\n-\u003e 4238                     raise ValueError\r\n   4239             except ValueError:\r\n\r\nValueError: \r\n\r\nDuring handling of the above exception, another exception occurred:\r\n\r\nValueError                                Traceback (most recent call last)\r\n\u003cipython-input-2-41dfae030a6e\u003e in \u003cmodule\u003e()\r\n      1 import matplotlib.pyplot as plt\r\n      2 f, ax = plt.subplots()\r\n----\u003e 3 ax.scatter([], [], c=[\"r\", \"b\", \"g\"])\r\n\r\n~/anaconda/envs/seaborn-dev/lib/python3.6/site-packages/matplotlib/__init__.py in inner(ax, data, *args, **kwargs)\r\n   1808                         \"the Matplotlib list!)\" % (label_namer, func.__name__),\r\n   1809                         RuntimeWarning, stacklevel=2)\r\n-\u003e 1810             return func(ax, *args, **kwargs)\r\n   1811 \r\n   1812         inner.__doc__ = _add_data_doc(inner.__doc__,\r\n\r\n~/anaconda/envs/seaborn-dev/lib/python3.6/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   4243                         \"acceptable for use with 'x' with size {xs}, \"\r\n   4244                         \"'y' with size {ys}.\"\r\n-\u003e 4245                         .format(nc=n_elem, xs=x.size, ys=y.size)\r\n   4246                     )\r\n   4247                 # Both the mapping *and* the RGBA conversion failed: pretty\r\n\r\nValueError: 'c' argument has 3 elements, which is not acceptable for use with 'x' with size 0, 'y' with size 0.\r\n```\r\n\r\nIMO this is an unnecessary exception because it conflicts with another patten in matplotlib, which is passing empty data along with specified style attributes (e.g. to create a proxy artist). I appreciate that the `c` parameter occupies a fuzzy zone between data and style attribute. But specifically in the case when the position data are *empty*, no points will have the wrong colors.","author":{"url":"https://github.com/mwaskom","@type":"Person","name":"mwaskom"},"datePublished":"2019-05-01T15:00:13.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":11},"url":"https://github.com/14113/matplotlib/issues/14113"}