René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"[DOC]: Using matplotlib.pyplot.pcolormesh with shading='flat'","articleBody":"### Bug summary\n\nWhen using plt.pcolormesh on an array of size C=(10,10), with two coordinates of size X=(10) and Y=(10), the last value C[-1,-1] isn't silently dropped as your documentation says.\n\nThe documentation :\n\"If X, Y and C have equal dimensions, a warning will be raised and the last row and column of C will be ignored.\"\nextracted from http://matplotlib.org/stable/api/_as_gen/matplotlib.pyplot.pcolormesh.html\n\nThe error I get when using xarrays wrapper of pcolormesh:\n``` bash\nTraceback (most recent call last):\n  File \"/home/AD278604/deltavar-GyselaX/test.py\", line 21, in \u003cmodule\u003e\n    da.plot.pcolormesh(shading=\"flat\", infer_intervals=False)\n    ~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^\n  File \"/data/gyselarunner/gyselalibxx-env-shared/.spack-env/view/lib/python3.14/site-packages/xarray/plot/accessor.py\", line 784, in pcolormesh\n    return dataarray_plot.pcolormesh(self._da, *args, **kwargs)\n           ~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^\n  File \"/data/gyselarunner/gyselalibxx-env-shared/.spack-env/view/lib/python3.14/site-packages/xarray/plot/dataarray_plot.py\", line 1606, in newplotfunc\n    primitive = plotfunc(\n        xplt,\n    ...\u003c7 lines\u003e...\n        **kwargs,\n    )\n  File \"/data/gyselarunner/gyselalibxx-env-shared/.spack-env/view/lib/python3.14/site-packages/xarray/plot/dataarray_plot.py\", line 2315, in pcolormesh\n    primitive = ax.pcolormesh(x, y, z, **kwargs)\n  File \"/data/gyselarunner/gyselalibxx-env-shared/.spack-env/view/lib/python3.14/site-packages/matplotlib/__init__.py\", line 1524, in inner\n    return func(\n        ax,\n        *map(cbook.sanitize_sequence, args),\n        **{k: cbook.sanitize_sequence(v) for k, v in kwargs.items()})\n  File \"/data/gyselarunner/gyselalibxx-env-shared/.spack-env/view/lib/python3.14/site-packages/matplotlib/axes/_axes.py\", line 6528, in pcolormesh\n    X, Y, C, shading = self._pcolorargs('pcolormesh', *args,\n                       ~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^\n                                        shading=shading, kwargs=kwargs)\n                                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^\n  File \"/data/gyselarunner/gyselalibxx-env-shared/.spack-env/view/lib/python3.14/site-packages/matplotlib/axes/_axes.py\", line 6060, in _pcolorargs\n    raise TypeError(f\"Dimensions of C {C.shape} should\"\n    ...\u003c2 lines\u003e...\n                    f\" see help({funcname})\")\nTypeError: Dimensions of C (2, 2) should be one smaller than X(2) and Y(2) while using shading='flat' see help(pcolormesh)\n```\n\n### Code for reproduction\n\n```Python\nimport xarray as xr\nimport numpy as np\nimport matplotlib.pyplot as plt\n\nC = np.array([[0, 1],\n              [2, 3]])\nX = [0, 1]\nY = [0, 1]\n\nda = xr.DataArray(\n    data=C,\n    coords={\"Y\": Y, \"X\": X},\n    dims=[\"Y\", \"X\"]\n)\n\nprint(\"Data shape:\", da.shape)\nprint(\"X shape:\", da[\"X\"].shape)\nprint(\"Y shape:\", da[\"Y\"].shape)\nprint(\"-\" * 50)\n\nda.plot.pcolormesh(shading=\"flat\", infer_intervals=False)\nplt.show()\n```\n\n### Actual outcome\n\n``` bash\nTraceback (most recent call last):\n  File \"/home/AD278604/deltavar-GyselaX/test.py\", line 21, in \u003cmodule\u003e\n    da.plot.pcolormesh(shading=\"flat\", infer_intervals=False)\n    ~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^\n  File \"/data/gyselarunner/gyselalibxx-env-shared/.spack-env/view/lib/python3.14/site-packages/xarray/plot/accessor.py\", line 784, in pcolormesh\n    return dataarray_plot.pcolormesh(self._da, *args, **kwargs)\n           ~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^\n  File \"/data/gyselarunner/gyselalibxx-env-shared/.spack-env/view/lib/python3.14/site-packages/xarray/plot/dataarray_plot.py\", line 1606, in newplotfunc\n    primitive = plotfunc(\n        xplt,\n    ...\u003c7 lines\u003e...\n        **kwargs,\n    )\n  File \"/data/gyselarunner/gyselalibxx-env-shared/.spack-env/view/lib/python3.14/site-packages/xarray/plot/dataarray_plot.py\", line 2315, in pcolormesh\n    primitive = ax.pcolormesh(x, y, z, **kwargs)\n  File \"/data/gyselarunner/gyselalibxx-env-shared/.spack-env/view/lib/python3.14/site-packages/matplotlib/__init__.py\", line 1524, in inner\n    return func(\n        ax,\n        *map(cbook.sanitize_sequence, args),\n        **{k: cbook.sanitize_sequence(v) for k, v in kwargs.items()})\n  File \"/data/gyselarunner/gyselalibxx-env-shared/.spack-env/view/lib/python3.14/site-packages/matplotlib/axes/_axes.py\", line 6528, in pcolormesh\n    X, Y, C, shading = self._pcolorargs('pcolormesh', *args,\n                       ~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^\n                                        shading=shading, kwargs=kwargs)\n                                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^\n  File \"/data/gyselarunner/gyselalibxx-env-shared/.spack-env/view/lib/python3.14/site-packages/matplotlib/axes/_axes.py\", line 6060, in _pcolorargs\n    raise TypeError(f\"Dimensions of C {C.shape} should\"\n    ...\u003c2 lines\u003e...\n                    f\" see help({funcname})\")\nTypeError: Dimensions of C (2, 2) should be one smaller than X(2) and Y(2) while using shading='flat' see help(pcolormesh)\n```\n\n### Expected outcome\n\nthe plot, and matplotlib silently dropping the last value of C\n\n### Additional information\n\n_No response_\n\n### Operating system\n\nDebian\n\n### Matplotlib Version\n\n3.10.7\n\n### Matplotlib Backend\n\nagg\n\n### Python version\n\n3.14\n\n### Jupyter version\n\n_No response_\n\n### Installation\n\npip","author":{"url":"https://github.com/ArielDeVora","@type":"Person","name":"ArielDeVora"},"datePublished":"2026-03-17T12:54:54.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":2},"url":"https://github.com/31320/matplotlib/issues/31320"}