René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"drawstyle with \"step\" has display error","articleBody":"### Bug report\r\n\r\n**Bug summary**\r\n\r\nWhen plotting with `drawstyle='steps'` (or `steps-pre`, `steps-mid`, or `steps-post`) there is a graphic display error. This was submitted to Pandas (https://github.com/pandas-dev/pandas/issues/31965) but I realize it may be a Matplotlib issue.\r\n\r\nSpecifically, on the graphic below and when using these two vectors:\r\n\r\n```\r\nx = [0,1,2]\r\ny = [0,1,2]\r\n```\r\n\r\n+ `steps-pre` and `steps` imply that the `y` values is 1 in `x=[0,1]`. I would argue that the proper way to interpret this data is that y = 0 at x = 0, and presumably remains at 0 until the y value is updated to 1 at x=1. These two options essentially drop the first data point. There is some indication of an (x,y) = (0,0), but it is minimal.\r\n+ `steps-post` has the same issue but at the end.\r\n+ `steps-mid` graphically weights the values unevenly. The `y=1` value has twice the weight of the other two line segments, based on length.\r\n+ The fifth panel is graphically correct in my opinion, but requires a modification of the data before plotting it.\r\n\r\n**Code for reproduction**\r\n\r\n```python\r\nimport matplotlib.pyplot as plt\r\n\r\nx = [0,1,2]\r\ny = [0,1,2]\r\n\r\nfig = plt.figure(1, figsize=(3,7))\r\n\r\nax = fig.add_subplot(611)\r\nax.plot(x,y, drawstyle='steps-pre')\r\nax.set_ylabel('steps-pre')\r\n\r\nax = fig.add_subplot(612)\r\nax.plot(x,y, drawstyle='steps')\r\nax.set_ylabel('steps')\r\n\r\nax = fig.add_subplot(613)\r\nax.plot(x,y, drawstyle='steps-mid')\r\nax.set_ylabel('steps-mid')\r\n\r\nax = fig.add_subplot(614)\r\nax.plot(x,y, drawstyle='steps-post')\r\nax.set_ylabel('steps-post')\r\n\r\nx.append(x[-1]+1)\r\ny.append(y[-1])\r\n\r\nax = fig.add_subplot(615)\r\nax.plot(x,y, drawstyle='steps-post')\r\nax.set_ylabel('steps-post\\nw/ extra data')\r\n```\r\n\r\n**Actual outcome**\r\n\r\n![steps-post](https://user-images.githubusercontent.com/145117/75714626-ec678d00-5c80-11ea-82f6-703026d1e85c.png)\r\n\r\n\r\n**Expected outcome**\r\n\r\nSee bottom panel.\r\n\r\nThe plot should display y[0] from x[0] to x[1], y[n] from x[n] to x[n+1], and therefore needs to have an x[n+1] appended to the end of the plot.","author":{"url":"https://github.com/mankoff","@type":"Person","name":"mankoff"},"datePublished":"2020-03-02T20:28:33.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":2},"url":"https://github.com/16635/matplotlib/issues/16635"}