Add new metrics for tf.keras

[AakashKumarNain]

Can we please add metrics as well to the tensorflow_addons directory? There are many metrics that are used on a daily basis by many Data Scientists/ML engineers but they are still not available in tf.keras. Some of them are:

• Cohen's Kappa
• IOU for bounding boxes
• f1/f-beta score

[armando-fandango]

Some of the other metrics/loss functions that could be added are for example pinball loss and SMAPE loss, both from the field of time-series.

[seanpmorgan]

Per our discussion in the monthly meeting this seems like it would be a good subpackage. To start we could begin by defining the API structure for the subpackage and an example metric. f1 score should be pretty easy to implement, seeing as precision and recall are already built in to tf.keras.metrics

[facaiy]

@AakashKumarNain Hi, Aakash, would you like to make a contribution? By the way, thank you for mentioning Cohen's Kappa, which was implemented by me, haha :-)

[AakashKumarNain]

@facaiy Sure. Actually, before I was aware of addons, I submitted a PR to TF repo. Check this tensorflow/tensorflow#25051 (comment)

[AakashKumarNain]

@facaiy We need to import class Metric(Layer) in keras_utils.py so that we can directly import it in the metrics subpackage without defining the class explicitly. It will be similar to how LossFunctionWrapper class has been imported. What do you say?

[facaiy]

I would say that it sounds reasonable. cc @seanpmorgan Sean, what do you think?

[seanpmorgan]

Yes, but it should also be included in our API issue sent to core. I'll be sure to include it and send the issue this week (was just waiting until we had a complete list... but that may never happen)

[AakashKumarNain]

@seanpmorgan @facaiy any updates on this?

[seanpmorgan]

https://github.com/tensorflow/tensorflow/blob/master/tensorflow/python/keras/metrics.py#L65 I believe its public now? Sorry I've built the list of exports we need, but I have to keep updating it as new APIs are released / want to make sure there are not alternatives

[AakashKumarNain]

Haha I haven't checked it yet @seanpmorgan but I will do it by tomorrow. Btw 1.14 cut was scheduled on 15th. So whatever is in that release, it should be public, right?