issues: 847006334

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id node_id number title user state locked assignee milestone comments created_at updated_at closed_at author_association active_lock_reason draft pull_request body reactions performed_via_github_app state_reason repo type
847006334 MDU6SXNzdWU4NDcwMDYzMzQ= 5097 2d plots may fail for some choices of `x` and `y` 3958036 closed 0     1 2021-03-31T17:26:34Z 2021-04-22T07:16:17Z 2021-04-22T07:16:17Z CONTRIBUTOR      

What happened: When making a 2d plot with a 1d x argument and a 2d y, if the two dimensions have the same size and are in the wrong order, no plot is produced - the third plot in the MCVE is blank.

What you expected to happen: All three plots in the MCVE should be identical.

Minimal Complete Verifiable Example:

```python from matplotlib import pyplot as plt import numpy as np import xarray as xr

ds = xr.Dataset({"z": (["x", "y"], np.random.rand(4,4))})

x2d, y2d = np.meshgrid(ds["x"], ds["y"])

ds = ds.assign_coords(x2d=(["x", "y"], x2d.T), y2d=(["x", "y"], y2d.T))

fig, axes = plt.subplots(1,3)

h0 = ds["z"].plot.pcolormesh(x="y2d", y="x2d", ax=axes[0]) h1 = ds["z"].plot.pcolormesh(x="y", y="x", ax=axes[1]) h2 = ds["z"].plot.pcolormesh(x="y", y="x2d", ax=axes[2])

plt.show() ```

result:

Anything else we need to know?:

The bug is present in both the 0.17.0 release and current master.

I came across this while starting to work on #5084. I think the problem is here https://github.com/pydata/xarray/blob/ddc352faa6de91f266a1749773d08ae8d6f09683/xarray/plot/plot.py#L678-L684 as the check xval.shape[0] == yval.shape[0] doesn't work if the single dimension of x is actually the second dimension of y, but happened to have the same size as the first dimension of y? I think it needs to check the actual dimensions of x and y.

Why don't we just do something like xval = xval.broadcast_like(darray) yval = yval.broadcast_like(darray) if either coordinate is 2d before using .values to convert to numpy arrays?

Environment:

Output of <tt>xr.show_versions()</tt> INSTALLED VERSIONS ------------------ commit: None python: 3.8.6 | packaged by conda-forge | (default, Oct 7 2020, 19:08:05) [GCC 7.5.0] python-bits: 64 OS: Linux OS-release: 5.4.0-70-generic machine: x86_64 processor: x86_64 byteorder: little LC_ALL: None LANG: en_GB.UTF-8 LOCALE: en_GB.UTF-8 libhdf5: 1.10.6 libnetcdf: 4.7.4 xarray: 0.17.0 pandas: 1.1.5 numpy: 1.19.4 scipy: 1.5.3 netCDF4: 1.5.5.1 pydap: None h5netcdf: None h5py: 3.1.0 Nio: None zarr: None cftime: 1.3.0 nc_time_axis: None PseudoNetCDF: None rasterio: None cfgrib: None iris: None bottleneck: None dask: 2020.12.0 distributed: 2020.12.0 matplotlib: 3.3.3 cartopy: None seaborn: None numbagg: None pint: 0.16.1 setuptools: 49.6.0.post20201009 pip: 20.3.3 conda: 4.9.2 pytest: 6.2.1 IPython: 7.19.0 sphinx: 3.4.0 
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