issues: 172290413

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id node_id number title user state locked assignee milestone comments created_at updated_at closed_at author_association active_lock_reason draft pull_request body reactions performed_via_github_app state_reason repo type
172290413 MDU6SXNzdWUxNzIyOTA0MTM= 978 broadcast() broken on dask backend 6213168 closed 0     4 2016-08-20T20:56:33Z 2016-12-09T20:28:42Z 2016-12-09T20:28:42Z MEMBER      

``` python

a = xarray.DataArray([1,2]).chunk(1) a <xarray.DataArray (dim_0: 2)> dask.array<xarray-..., shape=(2,), dtype=int64, chunksize=(1,)> Coordinates: * dim_0 (dim_0) int64 0 1 xarray.broadcast(a) (<xarray.DataArray (dim_0: 2)> array([1, 2]) Coordinates: * dim_0 (dim_0) int64 0 1,) ```

The problem is actually somewhere in the constructor of DataArray. In alignment.py:362, we have return DataArray(data, ...) where data is a Variable with dask backend. The returned DataArray object has a numpy backend. As a workaround, changing that line to return DataArray(data.data, ...) (thus passing a dask array) fixes the problem.

After that however there's a new issue: whenever broadcast adds a dimension to an array, it creates it in a single chunk, as opposed to copying the chunking of the other arrays. This can easily call a host to go out of memory, and makes it harder to work with the arrays afterwards because chunks won't match.

 
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