These return dicts of the indices of the minimum or maximum of a
DataArray over several dimensions.

When argmin or argmax are called with a sequence for 'dim', they now
return a dict with the indices for each dimension in dim.

If single dim is passed to Dataset.argmin() or Dataset.argmax(), then
pass through to _argmin_base or _argmax_base. If a sequence is passed
for dim, raise an exception, because the result for each DataArray would
be a dict, which cannot be stored in a Dataset.

The basic numpy-style argmin() and argmax() methods were renamed when
adding support for handling multiple dimensions in DataArray.argmin()
and DataArray.argmax(). Variable.argmin() and Variable.argmax() are
therefore renamed as Variable._argmin_base() and
Variable._argmax_base().

If a method (such as 'argmin') has been explicitly defined on a class
(so that hasattr(cls, "argmin")==True), then do not inject that method,
as it would override the explicitly defined one. Instead inject a
private method, prefixed by "_injected_" (such as '_injected_argmin'), so
that the injected method is available to the explicitly defined one.

Do not perform the hasattr check on binary ops, because this breaks
some operations (e.g. addition between DataArray and int in
test_dask.py).

Now not needed because of change to injection in ops.py.

Makes use of argmin and argmax more general (they are available for
Variable) and is straightforward for DataArray to wrap the Variable
version.

When np.argmin(da) is called, numpy passes an 'out' keyword argument to
argmin/argmax. Need to allow this argument to avoid errors (but an
exception is thrown if out is not None).

Co-Authored-By: keewis <keewis@users.noreply.github.com>

Co-Authored-By: keewis <keewis@users.noreply.github.com>

This reverts commit 8caf2b8.

… signature"

This reverts commit ab480b5.

Replaces need for "_injected_argmin" and "_injected_argmax".

Applying numpy functions to xarray objects is not necessarily expected
to work, and the wrapping of argmin() and argmax() is broken by
xarray-specific interface of argmin() and argmax() methods of Variable,
DataArray and Dataset.

Also, previously suggested workaround was not correct. Remove suggestion
as there is no workaround (but the removed behaviour is unlikely to be
useful).

Co-authored-by: Deepak Cherian <dcherian@users.noreply.github.com>

Pass an explicit axis or dim argument instead to avoid the warning.

Prefer to pass reduce_dims=None when possible, including for variables
with only one dimension. Avoids an error if an 'axis' keyword was
passed.

Co-authored-by: keewis <keewis@users.noreply.github.com>