Error: A list of 'ChoiceParameter' is not iterable

[Runyu-Zhang]

While creating a list of choice parameters using dictionary:
parameters_list = [dict(name = parameter,
type = "choice",
values = [x,...]
) for parameter in all_parameters
]
it has warning UserWarning: sort_values is not specified for ChoiceParameter "xxx". Defaulting to True for parameters of ParameterType FLOAT. To override this behavior (or avoid this warning), specify sort_values during ChoiceParameter construction.

So if I want to avoid those warnings by creating my parameters using ChoiceParameter:

from ax import ChoiceParameter, ParameterType

[ChoiceParameter(name = parameter,
parameter_type = ParameterType.FLOAT,
values =[x,...],
is_ordered = True,
sort_values = False) for parameter in all_parameters]
it becomes an error
experiment = self.make_experiment(
File "/ax/lib/python3.9/site-packages/ax/service/utils/instantiation.py", line 908, in make_experiment
search_space=cls.make_search_space(parameters, parameter_constraints),
File "/ax/lib/python3.9/site-packages/ax/service/utils/instantiation.py", line 687, in make_search_space
typed_parameters = [cls.parameter_from_json(p) for p in parameters]
File "/ax/lib/python3.9/site-packages/ax/service/utils/instantiation.py", line 687, in
typed_parameters = [cls.parameter_from_json(p) for p in parameters]
File "/ax/lib/python3.9/site-packages/ax/service/utils/instantiation.py", line 280, in parameter_from_json
if "parameter_type" in representation:
TypeError: argument of type 'ChoiceParameter' is not iterable

Although it's not critical, still better to have a way to pass "sort_values" through dict(), or having ChoiceParameter() iterable.

[mgrange1998]

Yes, looking through the ChoiceParameter construction code it looks like there isn't yet a way to pass "sort_values" with a dict, thanks for bringing this to our attention.

If I am understanding correctly, you are passing a "ChoiceParameter" object into "parameter_from_json", and line 280 is erroring because ChoiceParameter is not an iterable object. This is expected, as parameter_from_json is meant to convert JSON objects to Parameter objects.
Since you are now constructing the ChoiceParameter you do not need to pass it into parameter_from_json- you can instead use the ChoiceParameter directly. Let me know if this helps!

[Runyu-Zhang]

Thanks for the tips mgrange1998. But I guess my issue was that when I construct a list of "ChoiceParameter" using for loop, like:
list_choice_parameters = []
for parameter in all_parameters:
list_choice_parameters.append(ChoiceParameter(name = parameter,
parameter_type = ParameterType.FLOAT,
values =[x1, x2, ...],
is_ordered = True,
sort_values = False)
)
and then pass list_choice_parameters to ax_client.create_experiment(name = name,
parameters = list_choice_parameters,
objectives = objectives
)
this is throwing an error TypeError: argument of type 'ChoiceParameter' is not iterable

Instead, if I append dictionaries to "list_parameters=[]", and then pass to ax_client.create_experiment(), it is fine, but then the warning comes: sort_values is not specified for ChoiceParameter "xxx". Defaulting to True for parameters of ParameterType FLOAT. To override this behavior (or avoid this warning), specify sort_values during ChoiceParameter construction.
Hopefully it makes sense.

[mgrange1998]

Hello again- that makes sense to me. I have a pull request up which will fix your issue by allowing you to specify "sort_values" in the input dictionary #2231
Once this lands, you'll be able to specify "sort_values" explicitly to stop the UserWarning from appearing. Let me know if you have any other questions!

[Runyu-Zhang]

Nice. Thank you!