MCVE Code Sample

```python import xarray as xr import numpy as np

da = xr.DataArray( np.arange(56).reshape((7, 8)), coords={ 'x': list('abcdefg'), 'y': 10 * np.arange(8) }, dims=['x', 'y'] )

Shouldn't this be (2,)?

assert da.isel(x=[0, 1], y=[0, 1]).shape == (2, 2) ```

Expected Output

I had expected da.isel(x=[0, 1], y=[0, 1]) to have shape (2,). I had generally expected indexing with isel to behave more like numpy indexing. It's very possible I'm just missing something, or that this is more of a documentation issue more than a behavior issue.

Problem Description

Going off this example in #507:

python In [3]: da.isel_points(x=[0, 1, 6], y=[0, 1, 0], dim='points') Out[3]: <xray.DataArray (points: 3)> array([ 0, 9, 48]) Coordinates: y (points) int64 0 10 0 x (points) |S1 'a' 'b' 'g' * points (points) int64 0 1 2

and the deprecation of isel_points with isel, I had expected to get numpy-like coordinate indexing using isel.

This was made a little bit more confusing by the documentation for setting values by index. In particular the example:

```python In [68]: da[ind_x, ind_y] = -2 # assign -2 to (ix, iy) = (0, 0) and (1, 1)

In [69]: da Out[69]: <xarray.DataArray (x: 3, y: 4)> array([[-2, -2, -1, -1], [-2, -2, 6, 7], [ 8, 9, 10, 11]]) ```

To me, the comment # assign -2 to (ix, iy) = (0, 0) and (1, 1) makes it sound like values will be assigned at the coordinates (0, 0) and (1, 1), not (0, 0), (0, 1), (1, 0), and (1, 1).

All in all, I'm not sure if this is a bug, or an issue with documentation. If isel is not meant to behave like isel_points, it would be nice to see that in the documentation. If it is possible to get and set points by coordinate (without looping over single coordinates) it would be nice to see an example in the documentation where that's shown.

Output of xr.show_versions()

# Paste the output here xr.show_versions() here INSTALLED VERSIONS ------------------ commit: None python: 3.7.6 (default, Jan 4 2020, 12:18:30) [Clang 11.0.0 (clang-1100.0.33.16)] python-bits: 64 OS: Darwin OS-release: 19.3.0 machine: x86_64 processor: i386 byteorder: little LC_ALL: None LANG: en_US.UTF-8 LOCALE: en_US.UTF-8 libhdf5: 1.10.2 libnetcdf: 4.6.3 xarray: 0.15.0 pandas: 1.0.1 numpy: 1.18.1 scipy: 1.4.1 netCDF4: 1.5.2 pydap: None h5netcdf: 0.7.4 h5py: 2.10.0 Nio: None zarr: 2.4.0 cftime: 1.0.3.4 nc_time_axis: None PseudoNetCDF: None rasterio: None cfgrib: None iris: None bottleneck: None dask: 2.9.2 distributed: 2.9.3 matplotlib: 3.1.3 cartopy: None seaborn: 0.10.0 numbagg: None setuptools: 45.2.0 pip: 20.0.2 conda: None pytest: 5.3.4 IPython: 7.11.1 sphinx: 2.3.1