Expose Precision and Recall to user via TeacherMetrics

[prajjwal1]

Patch description
Considering that other metrics such as ctpb, ctrunc, ctrunclen (less frequently used by user) are exposed, it makes a lot of sense to expose precision and recall as they are internally being computed.

[stephenroller]

This is cool but I think it will be slow from recomputing these values?

[prajjwal1]

The way this function is setup, extracting f, p and r all at once will break other functionalities. I've been using it for sometime now, doesn't seem to add much overhead. Most of the time bs is set to <256, so should be fine. I can make it return all three things with one run, but then some other things will have to be changed. Do you have suggestions ?

[prajjwal1]

Or I can make "f1" default. If the user wants, they can print precision and recall themselves by passing the mode to output parameter.

[prajjwal1]

@stephenroller Can you please provide what you think based on the reply ?

[stephenroller]

Sorry; compute and return all 3 metrics in a generalization of the existing utility method. The caller will be responsible for separating and accumulating them.

[prajjwal1]

@stephenroller Is it fine now ? We only compute p, r and f1 only once now. So runtime is not affected.

[prajjwal1]

@klshuster Can you please take a look ?

[klshuster]

this looks great. could you please update the metrics master list (https://github.com/facebookresearch/ParlAI/blob/main/parlai/core/metrics.py#L53) to have the new metrics, and also please rename 'precision' and 'recall' to refer to the fact that they are computed based on unigrams (e.g., uni_prec)