René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"[Bug]: stackplot creates artifacts when height of input is zero","articleBody":"### Bug summary\n\nIn some cases, when a given input for `stackplot` has zero value entries, thin lines are drawn.\n\n### Code for reproduction\n\n```python\nimport numpy as np\r\nimport matplotlib.pyplot as plt\r\n\r\nnp.random.seed(42)\r\nx = np.arange(10)\r\ny0 = np.linspace(0, 1, 10)\r\ny1 = np.linspace(0, 1, 10)\r\ny2 = [0, 0, 0.25, 0, 0, 0, 0.25, 0, 0, 0]\r\ny3 = np.linspace(0, 1, 10)\r\n\r\n\r\ncolors=['grey', 'blue', 'red', 'blue']\r\n\r\ny = np.stack([y0, y1, y2, y3])\r\nim = plt.stackplot(x, y, colors=colors, lw=0)\n```\n\n\n### Actual outcome\n\n![image](https://user-images.githubusercontent.com/17513791/152529817-df3eb281-a437-43de-93e4-adf2c28d2106.png)\r\n\r\nOne can see thin grey lines where the red object hast zero height.\n\n### Expected outcome\n\n![image](https://user-images.githubusercontent.com/17513791/152530130-5044f09b-a5b1-4804-8864-441d762368a1.png)\r\n\r\nThe thin lines are gone\n\n### Additional information\n\nThis only happens when the color above and below the empty data has the same color, but there are some use-cases where this is needed (see e.g. [fish plots for evolutionary relationships](https://i.stack.imgur.com/hNl5C.png)).\r\n\r\n\r\n# Fix\r\nThe individual calls to `fill_between` need to have the following parameters:\r\n`where=(stack[i, :] != stack[i+1, :])`, ` interpolate=True` and `edgecolor=color`.\r\n\r\nThese are the changes made to `matplotlib/lib/matplotlib/stackplot.py`\r\n```python\r\n    # Color between x = 0 and the first array.\r\n    color = ax._get_lines.get_next_color()\r\n    coll = ax.fill_between(x, 0, stack[0, :],\r\n                                      where=(stack[0, :] != 0), interpolate=True, edgecolor=color,\r\n                                     facecolor=color, label=next(labels, None), **kwargs)\r\n    coll.sticky_edges.y[:] = [0]\r\n    r = [coll]\r\n\r\n    # Color between array i-1 and array i\r\n    for i in range(len(y) - 1):\r\n        color = ax._get_lines.get_next_color()\r\n        r.append(ax.fill_between(x, stack[i, :], stack[i+1, :],  \r\n                                               where=(stack[i, :] != stack[i+1, :]), interpolate=True, edgecolor=color,\r\n                                               facecolor=color, label=next(labels, None), **kwargs))\r\n```\r\n\r\nThese changes get rid of the lines but as far as I tested it do not have side effects for other plots. Probably one should check whether edgecolor is set in `**kwargs` as well.\n\n### Operating system\n\n_No response_\n\n### Matplotlib Version\n\n3.4.3\n\n### Matplotlib Backend\n\n_No response_\n\n### Python version\n\n_No response_\n\n### Jupyter version\n\n_No response_\n\n### Installation\n\nconda","author":{"url":"https://github.com/tlkaufmann","@type":"Person","name":"tlkaufmann"},"datePublished":"2022-02-04T12:52:29.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":7},"url":"https://github.com/22393/matplotlib/issues/22393"}