I tried to use apply_ufunc for a function that takes input of unequal length and requires vectorize=True which resulted in a ValueError. I think the problem stems from the way np.vectorize is called.

MCVE Code Sample

```python import xarray as xr import scipy as sp import scipy.stats import numpy as np

create dataarrays of unequal length

ds = xr.tutorial.open_dataset("air_temperature")

da1 = ds.air da2 = ds.air.isel(time=slice(None, 50))

function that takes arguments of unequal length and requires vectorizing

def mannwhitneyu(x, y): _, p = sp.stats.mannwhitneyu(x, y) return p

test that the function takes arguments of unequal length

mannwhitneyu(da1.isel(lat=0, lon=0), da2.isel(lat=0, lon=0))

xr.apply_ufunc( mannwhitneyu, da1, da2, input_core_dims=[["time"], ["time"]], exclude_dims=set(["time"]), vectorize=True, )

```

Returns

python ValueError: inconsistent size for core dimension 'n': 50 vs 2920 Note: the error stems from numpy.

Expected Output

A DataArray.

Problem Description

I can reproduce the problem in pure numpy:

python vec_wrong = np.vectorize(mannwhitneyu, signature="(n),(n)->()", otypes=[np.float]) vec_wrong(da1.values.T, da2.values.T)

The correct result is returned when the signature is changed: python vec_correct = np.vectorize(mannwhitneyu, signature="(m),(n)->()", otypes=[np.float]) vec_correct(da1.values.T, da2.values.T) So I think the signature needs to be changed when exclude_dims are present.

Versions

Output of `xr.show_versions()`

This is my development environment, so i think xarray should be 'master'. **PNC:/home/mathause/conda/envs/xarray_devel/lib/python3.7/site-packages/PseudoNetCDF/pncwarn.py:24:UserWarning: pyproj could not be found, so IO/API coordinates cannot be converted to lat/lon; to fix, install pyproj or basemap (e.g., `pip install pyproj)` INSTALLED VERSIONS ------------------ commit: None python: 3.7.3 | packaged by conda-forge | (default, Jul 1 2019, 21:52:21) [GCC 7.3.0] python-bits: 64 OS: Linux OS-release: 4.15.0-91-generic machine: x86_64 processor: x86_64 byteorder: little LC_ALL: None LANG: en_US.UTF-8 LOCALE: en_US.UTF-8 libhdf5: 1.10.5 libnetcdf: 4.7.1 xarray: 0.11.1+335.gb0c336f6 pandas: 0.25.3 numpy: 1.17.3 scipy: 1.3.1 netCDF4: 1.5.3 pydap: installed h5netcdf: 0.7.4 h5py: 2.10.0 Nio: None zarr: 2.3.2 cftime: 1.0.4.2 nc_time_axis: None PseudoNetCDF: installed rasterio: 1.1.0 cfgrib: 0.9.5.4 iris: None bottleneck: 1.2.1 dask: 2.6.0 distributed: 2.6.0 matplotlib: 3.1.2 cartopy: None seaborn: 0.9.0 numbagg: None setuptools: 41.6.0.post20191101 pip: 19.3.1 conda: installed pytest: 5.2.2 IPython: 7.9.0 sphinx: None