Drawing only one contour in FacetGrid

[kuchaale]

MCVE Code Sample

import numpy as np
import matplotlib.pyplot as plt
import xarray as xr

x, y = np.meshgrid(np.arange(12), np.arange(12))
z = xr.DataArray(np.sqrt(x**2 + y**2))
z2 = xr.DataArray(np.sqrt(x**2 + y**2)+1)
ds = xr.concat([z,z2], dim = 'time')
ds['time'] = [0,1]

f, ax = plt.subplots()
ds[0].plot.contour(ax = ax, levels=[4], colors=['k'])
f, ax = plt.subplots()
ds[1].plot.contour(ax = ax, levels=[4], colors=['k'])
ds.plot.contour(col = 'time', levels=[4], colors=['k'])

Output

Expected Output

Problem Description

While drawing only one contour was fixed some time ago (#866), single contour plots in FacetGrid do not work for me.

Output of xr.show_versions()

INSTALLED VERSIONS ------------------ commit: None python: 3.6.8 (default, Oct 7 2019, 12:59:55) [GCC 8.3.0] python-bits: 64 OS: Linux OS-release: 4.15.0-65-generic machine: x86_64 processor: x86_64 byteorder: little LC_ALL: None LANG: en_US.UTF-8 LOCALE: en_US.UTF-8 libhdf5: 1.10.2 libnetcdf: 4.6.3

xarray: 0.14.1
pandas: 0.24.2
numpy: 1.17.3
scipy: 1.2.1
netCDF4: 1.5.1.2
pydap: installed
h5netcdf: 0.7.4
h5py: 2.9.0
Nio: None
zarr: 2.3.2
cftime: 1.0.3.4
nc_time_axis: 1.2.0
PseudoNetCDF: None
rasterio: 1.0.5
cfgrib: 0.9.6.2
iris: None
bottleneck: 1.2.1
dask: 2.6.0
distributed: 2.6.0
matplotlib: 3.0.3
cartopy: 0.16.0
seaborn: 0.9.0
numbagg: None
setuptools: 41.0.1
pip: 19.3.1
conda: None
pytest: 4.4.1
IPython: 7.1.1
sphinx: 2.0.1

[dcherian]

Thanks for the report. I'll mark this as a bug. PRs welcome!