issue_comments

Sorry for slow reply, I got pulled onto another task before Christmas and forgot to revisit. Hit this in a different way again today. I get a combo of mangled as well as NaN values.

``` print((d0.swe.y - d1.swe.y).shape == d0.swe.shape) print((d0.swe.y - d1.swe.y).shape) print(d0.swe.y.shape)

False (2509,) (2509,) ```

``` np.unique(d0.swe.y.values == d1.swe.y.values)

array([ True]) ```

``` np.unique(d0.swe.x.values == d1.swe.x.values)

array([False, True] xr.align(d0, d1, join="exact") ValueError: cannot align objects with join='exact' where index/labels/sizes are not equal along these coordinates (dimensions): 'x' ('x',) ```

Looking at x shows X off by 1e-12 np.unique(d0.swe.x.values - d1.swe.x.values) array([-1.62003744e-12, -1.60582658e-12, -1.59161573e-12, -1.57740487e-12, -1.56319402e-12, -1.54898316e-12, -1.53477231e-12, -1.52056145e-12, -1.50635060e-12, -1.49213975e-12, -1.47792889e-12, -1.46371804e-12, -1.44950718e-12, -1.43529633e-12, -1.42108547e-12, -1.40687462e-12, -1.39266376e-12, -1.37845291e-12, -1.36424205e-12, -1.35003120e-12, -1.33582034e-12, -1.32160949e-12, -1.30739863e-12, -1.29318778e-12, -1.27897692e-12, -1.26476607e-12, -1.25055521e-12, -1.23634436e-12, -1.22213351e-12, -1.20792265e-12, -1.19371180e-12, -1.17950094e-12, -1.16529009e-12, -1.15107923e-12, -1.13686838e-12, -1.12265752e-12, -1.10844667e-12, -1.09423581e-12, -1.08002496e-12, -1.06581410e-12, -1.05160325e-12, -1.03739239e-12, -1.02318154e-12, -1.00897068e-12, -9.94759830e-13, -9.80548975e-13, -9.66338121e-13, -9.52127266e-13, -9.37916411e-13, -9.23705556e-13, -9.09494702e-13, -8.95283847e-13, -8.81072992e-13, -8.66862138e-13, -8.52651283e-13, -8.38440428e-13, -8.24229573e-13, -8.10018719e-13, -7.95807864e-13, -7.81597009e-13, -7.67386155e-13, -7.53175300e-13, -7.38964445e-13, -7.24753590e-13, -7.10542736e-13, -6.96331881e-13, -6.82121026e-13, -6.67910172e-13, -6.53699317e-13, -6.39488462e-13, -6.25277607e-13, -6.11066753e-13, -5.96855898e-13, -5.82645043e-13, -5.68434189e-13, -5.54223334e-13, -5.40012479e-13, -5.25801624e-13, -5.11590770e-13, -4.97379915e-13, -4.83169060e-13, -4.68958206e-13, -4.54747351e-13, -4.40536496e-13, -4.26325641e-13, -4.12114787e-13, -3.97903932e-13, -3.83693077e-13, -3.69482223e-13, -3.55271368e-13, -3.41060513e-13, -3.26849658e-13, -3.12638804e-13, -2.98427949e-13, -2.84217094e-13, -2.70006240e-13, -2.55795385e-13, -2.41584530e-13, -2.27373675e-13, -2.13162821e-13, -1.98951966e-13, -1.84741111e-13, -1.70530257e-13, -1.56319402e-13, -1.42108547e-13, -1.27897692e-13, -1.13686838e-13, -9.94759830e-14, -8.52651283e-14, -7.10542736e-14, -5.68434189e-14, -4.26325641e-14, -2.84217094e-14, -1.42108547e-14, 0.00000000e+00])

I suspect there are floating point inaccuracies which can sometimes trip up xarray. But I would also not expect differences when the coords are created with the same piece of code.

Unfortunately your test does not work - it will first align and then do the subtraction... Any of the following should work:

python (d0.y - d1.y).shape == d0.shape d0.y.values == d1.y.values xr.align(d0, d1, join="exact")

If this worked earlier

Each tiff is generated from the same underlying code so they are expected (and should be) exactly identical. I haven't seen any indication they are different. I just double checked and the two in the example above indicate they are the same

is xarray sensitive in a way that wouldn't be obvious with this kind of test?

Could it be that the coordinates of the individual arrays are not exactly the same?

Further investigation suggests this is similar / related to Issue #3681. Using join="override" seems to resolve the problem. However, it is not at all clear why this needs to be done or why it "fixes" the problem. Is this intended behaviour?

edit: An old xarray 0.15.1 doesn't exhibit this behaviour and is correctly concated as expected.