Is it possible to add the option of modifying what happens when there is a tie in the rank? (If you want I can create a separate issue for this)

I think this can be done using the scipy rankdata function instead of the bottleneck rank (but also I think that adding the method option for the bottleneck package is also possible).

Small example: ```py

arr = xarray.DataArray( dask.array.random.random((11, 10), chunks=(3, 2)), coords={'a': list(range(11)), 'b': list(range(10))} )

def rank(x: xarray.DataArray, dim: str, method: str): # This option generate less tasks, I don't know why

axis = x.dims.index(dim)
return xarray.DataArray(
    dask.array.apply_along_axis(
        rankdata,
        axis,
        x.data,
        dtype=float,
        shape=(x.sizes[dim], ),
        method=method
    ),
    coords=x.coords,
    dims=x.dims
)

def rank2(x: xarray.DataArray, dim: str, method: str): from scipy.stats import rankdata

axis = x.dims.index(dim)
return xarray.apply_ufunc(
    rankdata,
    x.chunk({dim: x.sizes[dim]}),
    dask='parallelized',
    kwargs={'method': method, 'axis': axis},
    meta=x.data._meta
)

arr_rank1 = rank(arr, 'a', 'ordinal') arr_rank2 = rank2(arr, 'a', 'ordinal')

assert arr_rank1.equals(arr_rank2) ```

```py

Probably this can work for ranking arrays with nan values

def _nanrankdata1(a, method): y = np.empty(a.shape, dtype=np.float64) y.fill(np.nan) idx = ~np.isnan(a) y[idx] = rankdata(a[idx], method=method) return y

```