René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Duplicate legend labels with different colors can often result in an error.","articleBody":"\u003c!--To help us understand and resolve your issue, please fill out the form to the best of your ability.--\u003e\r\n\u003c!--You can feel free to delete the sections that do not apply.--\u003e\r\n\r\n### Bug report\r\n\r\nIf one makes a scatter plot (or a line graph) having multiple points with different markers and colors, but the same label, this will result in an error in version 2.1.1 (but not 2.1.0). A small example is provided below:\r\n\r\n**Code for reproduction**\r\n\r\n```\r\n#!/usr/bin/env python\r\nimport matplotlib as mpl\r\nmpl.use('Agg')\r\nimport matplotlib.pyplot as plt\r\n\r\ncolor='#00ff00ff'\r\nplt.scatter(0.0, 1.0, color=color, marker='o', label='test')\r\ncolor='#00ffaaff'\r\nplt.scatter(0.5, 0.0, color=color, marker='v', label='test')\r\nplt.legend()\r\nplt.savefig('foo.png')\r\n```\r\n\r\n**Actual outcome**\r\n\r\nThis example uses a scatter plot, but the same issue *can* arise with line plots if one uses a numpy vector as a color (e.g., `[0.0, 1.0, 0.0, 1.0]`). The error produced for the above example is as follows:\r\n\r\n```\r\nTraceback (most recent call last):\r\n  File \"foo.py\", line 11, in \u003cmodule\u003e\r\n    plt.legend()\r\n  File \"/home/ryan/.local/lib/python2.7/site-packages/matplotlib/pyplot.py\", line 3748, in legend\r\n    ret = gca().legend(*args, **kwargs)\r\n  File \"/home/ryan/.local/lib/python2.7/site-packages/matplotlib/axes/_axes.py\", line 498, in legend\r\n    **kwargs)\r\n  File \"/home/ryan/.local/lib/python2.7/site-packages/matplotlib/legend.py\", line 1402, in _parse_legend_args\r\n    handles, labels = _get_legend_handles_labels(axs, handlers)\r\n  File \"/home/ryan/.local/lib/python2.7/site-packages/matplotlib/legend.py\", line 1360, in _get_legend_handles_labels\r\n    and not _in_handles(handle, label)):\r\n  File \"/home/ryan/.local/lib/python2.7/site-packages/matplotlib/legend.py\", line 1344, in _in_handles\r\n    if f_h.get_facecolor() != h.get_facecolor():\r\nValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all()\r\n```\r\n\r\nAt the end of the day, this ends up being because the face (and edge) colors are converted to a numpy vector, which can't be compared with `!=` since they have multiple elements. With the help of `git bisect`, I've tracked this down to [this commit at the end of October](https://github.com/matplotlib/matplotlib/commit/4f594f4d735ac1540d043b4843f9247111c5a6b6).\r\n\r\nNow I'll grant that this only happens if people use the same label for multiple symbols/lines, which is a bad idea...but one can't always prevent end users from doing that.\r\n","author":{"url":"https://github.com/dpryan79","@type":"Person","name":"dpryan79"},"datePublished":"2017-12-20T13:20:12.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":4},"url":"https://github.com/10053/matplotlib/issues/10053"}