Wrong dimension referenced in boolean indexing with .loc

[d-chambers]

I am using Ubuntu 16, python 3.6, and xarary 0.9.5.

import numpy as np
import xarray as xr

# setup for a simple grid
DX = 50
X = np.arange(0, 2010, DX)
Y = np.arange(0, 2010, DX)
Z = np.arange(0, 2010, DX)
grid_shape = (len(X), len(Y), len(Z))

# Create data array
dims = 'X Y Z'.split()
coords = {'X': X, 'Y': Y, 'Z': Z}
dar = xr.DataArray(np.ones(grid_shape), dims=dims, coords=coords)

# slice the data array so that all Z values are greater than 1000
dar2 = dar.loc[dar.Z > 1000]
assert np.all(dar2.Z > 1000)  # fails becase dar is sliced along X, not Z

Since the object returned from dar.Z > 1000 is a data array with "Z" as the only dim I would expect this to slice the "Z" dim rather than X.

[d-chambers]

I should point out It does work when I specify the dimension with a dict:

dar2 = dar.loc[{'Z': dar.Z > 1000}]
assert np.all(dar2.Z > 1000)  # doesn't raise

[shoyer]

Xarray's indexing currently ignores dimension/index labels, which I agree is not ideal (and can lead to surprising behavior like this): #974

Another work-around is to use where, e.g., dar.where(dar.Z > 1000).

[shoyer]

Fixed by #1639