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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
779938616 MDU6SXNzdWU3Nzk5Mzg2MTY= 4770 Interpolation always returns floats Illviljan 14371165 open 0     1 2021-01-06T03:16:43Z 2021-01-12T16:30:54Z   MEMBER      

What happened: When interpolating datasets integer arrays are forced to floats.

What you expected to happen: To retain the same dtype after interpolation.

Minimal Complete Verifiable Example:

```python import numpy as np import dask.array as da a = np.arange(0, 2) b = np.core.defchararray.add("long_variable_name", a.astype(str)) coords = dict(time=da.array([0, 1])) data_vars = dict() for v in b: data_vars[v] = xr.DataArray( name=v, data=da.array([0, 1], dtype=int), dims=["time"], coords=coords, ) ds1 = xr.Dataset(data_vars)

print(ds1) Out[35]: <xarray.Dataset> Dimensions: (time: 4) Coordinates: * time (time) float64 0.0 0.5 1.0 2.0 Data variables: long_variable_name0 (time) int32 dask.array<chunksize=(4,), meta=np.ndarray> long_variable_name1 (time) int32 dask.array<chunksize=(4,), meta=np.ndarray>

Interpolate:

ds1 = ds1.interp( time=da.array([0, 0.5, 1, 2]), assume_sorted=True, method="linear", kwargs=dict(fill_value="extrapolate"), )

dask array thinks it's an integer array:

print(ds1.long_variable_name0) Out[55]: <xarray.DataArray 'long_variable_name0' (time: 4)> dask.array<dask_aware_interpnd, shape=(4,), dtype=int32, chunksize=(4,), chunktype=numpy.ndarray> Coordinates: * time (time) float64 0.0 0.5 1.0 2.0

But once computed it turns out is a float:

print(ds1.long_variable_name0.compute()) Out[38]: <xarray.DataArray 'long_variable_name0' (time: 4)> array([0. , 0.5, 1. , 2. ]) Coordinates: * time (time) float64 0.0 0.5 1.0 2.0

```

Anything else we need to know?: An easy first step is to also force np.float_ in da.blockwise in missing.interp_func.

The more difficult way is to somehow be able to change back the dataarrays into the old dtype without affecting performance. I did a test simply adding .astype()to the returned value in missing.interp and it doubled the calculation time.

I was thinking the conversion to floats in scipy could be avoided altogether by adding a (non-)public option to ignore any dtype checks and just let the user handle the "unsafe" interpolations.

Related: https://github.com/scipy/scipy/issues/11093

Environment:

Output of <tt>xr.show_versions()</tt> xr.show_versions() INSTALLED VERSIONS ------------------ commit: None python: 3.8.5 (default, Sep 3 2020, 21:29:08) [MSC v.1916 64 bit (AMD64)] python-bits: 64 OS: Windows libhdf5: 1.10.4 libnetcdf: None xarray: 0.16.2 pandas: 1.1.5 numpy: 1.17.5 scipy: 1.4.1 netCDF4: None pydap: None h5netcdf: None h5py: 2.10.0 Nio: None zarr: None cftime: None nc_time_axis: None PseudoNetCDF: None rasterio: None cfgrib: None iris: None bottleneck: 1.3.2 dask: 2020.12.0 distributed: 2020.12.0 matplotlib: 3.3.2 cartopy: None seaborn: 0.11.1 numbagg: None pint: None setuptools: 51.0.0.post20201207 pip: 20.3.3 conda: 4.9.2 pytest: 6.2.1 IPython: 7.19.0 sphinx: 3.4.0 
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     xarray 13221727 issue

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