pydata
`Dataset.broadcast_like(other)` should broadcast against like variables in other
Is your feature request related to a problem?
I am a bit puzzled about how xarrays is broadcasting Datasets. It seems to always add all dimensions to all variables. Is this what you want in general?
See this example:
import xarray as xr
da = xr.DataArray([[1, 2, 3]], dims=("x", "y"))
# <xarray.DataArray (x: 1, y: 3)>
# array([[1, 2, 3]])
ds = xr.Dataset({"a": ("x", [1]), "b": ("z", [2, 3])})
# <xarray.Dataset>
# Dimensions: (x: 1, z: 2)
# Dimensions without coordinates: x, z
# Data variables:
# a (x) int32 1
# b (z) int32 2 3
ds.broadcast_like(da)
# returns:
# <xarray.Dataset>
# Dimensions: (x: 1, y: 3, z: 2)
# Dimensions without coordinates: x, y, z
# Data variables:
# a (x, y, z) int32 1 1 1 1 1 1
# b (x, y, z) int32 2 3 2 3 2 3
# I think it should return:
# <xarray.Dataset>
# Dimensions: (x: 1, y: 3, z: 2)
# Dimensions without coordinates: x, y, z
# Data variables:
# a (x, y) int32 1 1 1 # notice here without "z" dim
# b (x, y, z) int32 2 3 2 3 2 3
Describe the solution you'd like
I would like broadcasting to behave the same way as e.g. a simple addition.
In the upper example da + ds produces the dimensions that I want.
Describe alternatives you've considered
ds + xr.zeros_like(da) this works, but seems more like a "dirty hack".
Additional context
Maybe one can add an option to broadcasting that controls this behavior?
see also #6304 which covers
xr.broadcast
I tried adding a join input to Dataset.broadcast_like and passing it to align, but that did not work (at least for join="inner"). Still got the same result...
I keep misunderstanding this issue so typing this out to make sure I got it right.
Writing out dimension names in square brackets
ds['a': 'x', 'b': 'z'].broadcast_like(da: ['x', 'y']) -> ds['a': ['x', y'], 'b': ['x', 'y', 'z']]
IIUC the request is to avoid broadcasting the variables in ds against each other, and to only broadcast each variable against da separately. Did I get it right?
@mjwillson posted a nice summary in #10031 :
I had to summarize the overall problem, it's that behaviour of xarray.broadcast (and Dataset.broadcast_like etc) is not consistent with how actual arithmetic operations broadcast, in cases where Datasets are involved.
In the light of #10031, and broadcasting a dataset to itself not behaving as a no-op, should we label this as "bug" rather than "enhancement"?
I found a use-case for broadcasting a dataset like requested: When trying to change values in-place, this only works if the replacement values are already broadcasted. An example can be found here: https://github.com/pydata/xarray/blob/main/xarray/computation/computation.py#L842 where instead of broadcasting I had to resort to adding a zero-valued dataset.