'Check if each element of self is an of ``container``.
Parameters
container : object
An object implementing a __contains__ to call on each element of
``self``.
Returns
is_contained : np.ndarray[bool]
An array with the same shape as self indicating whether each
element of self was an element of ``container``.'

@preprocess(container=coerce((list, tuple, np.ndarray), set))
def element_of(self, container):

    return self.map_predicate(container.__contains__)
