issue_comments

If there are conflicts in dimension coordinate, should it be outer join?

Consider this example: a = Dataset({ 'x': [10, 20], 'd1': ('x', [100, 200]), 'd2': ('x', [300, 400]) }) b = Dataset({ 'x': [15], 'd1': ('x', [500]), }) a.update(b) In the above, with anything but an outer join you're destroying d2 - which doesn't even exist in the rhs dataset! A sane, desirable outcome should be Dataset({ 'x': [10, 20, 15], 'd1': ('x', [nan, nan, 500]), 'd2': ('x', [300, 400, nan]) })

If there are no conflicts in dimension coordinate, but there are conflicts in non dimension coordinate, whether left or right should be prioritized?

I think this should be a right join. I alway think of non-index coords as N-to-1 properties of the index. For example, a = Dataset( coords={ 'country': ('country', ['UK', 'France', 'Greece']), 'currency': ('country', ['GBP', 'EUR', 'EUR']), }, data_vars={ 'GDP': ('country', [1000, 2000, 3000]), 'Debt': ('country', [100, 200, 300]), }) b = Dataset( # Greece exits the Eurozone coords={ 'country': ('country', ['UK', 'France', 'Greece']), 'currency': ('country', ['GBP', 'EUR', 'GRD']), }, data_vars={ 'GDP': ('country', [1000, 2000, 150000]), }) a.update(b) In the above example, I just broke the Debt variable - as I forgot to perform a currency conversion for the greek debt, which has been silently changed from 300 EUR to 300 GRD. However I can't see any elegant way to avoid this. I definitely would not like to duplicate the 'country' index.

Then I'm not sure I understand the change: fridge = xarray.Dataset( data_vars={ 'fruits': ('fruit', [10]), }, coords={ 'fruit': ('fruit', ['apples']), 'quality': ('fruit', ['Red Velvet']), }) shopping = xarray.Dataset( data_vars={ 'fruits': ('fruit', [20]), }, coords={ 'fruit': ('fruit', ['oranges']), 'quality': ('fruit', ['Tangerine']), }) fridge.update(shopping) # throw away old contents and fill with new stuff In both 0.10.3 and 0.10.4: <xarray.Dataset> Dimensions: (fruit: 1) Coordinates: * fruit (fruit) object 'apples' quality (fruit) object nan Data variables: fruits (fruit) float64 nan The above doesn't make any sense to me. I wanted to replace the fruits variable with brand new content, and instead I lost both the old and the new?!?

I'm of the strong opinion that all joins should be outer joins unless the user explicitly says otherwise, as it's the approach least prone to do damage. I would humbly suggest considering the change for a future major release (0.11 / 0.12), with several minor releases before that printing futurewarnings.

This said, I think that changing from a right join (0.10.3) to a left join (0.10.4) will only cause breakages without providing any actual benefit in terms of user-friendliness, so we should retain the previous behaviour. A right join vaguely makes more sense IMHO as it follows the general phylosophy of dict.update() where rhs wins in case of collision.