datacollector: enable getting nested attributes

[philip928lin]

I try to have a model_reporters to access nested attributes like {"Col1": "a.b.c.d"}.
The current reporter will return None as the default for getattr().
One solution I found is to substitute getattr() at line 175 of the datacollection module to rgetattr() shown below.

import functools
def rgetattr(obj, attr, *args):
    def _getattr(obj, attr):
        return getattr(obj, attr, *args)
    return functools.reduce(_getattr, [obj] + attr.split('.'))

This will do the trick. Source: https://stackoverflow.com/questions/31174295/getattr-and-setattr-on-nested-subobjects-chained-properties

New code for collect():

def collect(self, model):
        """Collect all the data for the given model object."""
        def rgetattr(obj, attr, *args):
            def _getattr(obj, attr):
                return getattr(obj, attr, *args)
            return reduce(_getattr, [obj] + attr.split('.'))
        if self.model_reporters:
            for var, reporter in self.model_reporters.items():
                # Check if Lambda operator
                if isinstance(reporter, types.LambdaType):
                    self.model_vars[var].append(reporter(model))
                # Check if model attribute
                elif isinstance(reporter, str):
                    #self.model_vars[var].append(getattr(model, reporter, None))
                    self.model_vars[var].append(rgetattr(model, reporter, None))
                # Check if function with arguments
                elif isinstance(reporter, list):
                    self.model_vars[var].append(reporter[0](*reporter[1]))
                # TODO: Check if method of a class, as of now it is assumed
                # implicitly if the other checks fail.
                else:
                    self.model_vars[var].append(reporter())

        if self.agent_reporters:
            agent_records = self._record_agents(model)
            self._agent_records[model.schedule.steps] = list(agent_records)

[rht]

I'm not sure if the use case is common to the point that this should be in the library. In the meantime, you can define rgetattr in the model file, and do {"Col1": rgetattr("a.b.c.d")}.

[philip928lin]

Sounds good.
The code will look like {"Col1": [rgetattr, [self, "a.b.c.d"]]}.
My code uses DotMap to incorporate sophisticated data and model structure. Therefore, I have a nested attribute structure.
I agree with you that we don't know how often other people will appreciate the same feature.
Thank you for your prompt reply!