Zhang's metric for association rules

[zuari1993]

• Current the in frequent_patterns/association_rules/metrics has support, confidence, lift, leverage, conviction.
• It is missing Zhang's metric.
• Zhang's metric is widely used in Industrial setting, particularly when you want to study dissociation also (other metrics only measure association)
• It would be great to add Zhang's metric.

Additional context

Research paper on Zhang's metric:
https://www.tandfonline.com/doi/pdf/10.1080/08839510903208062

The values range between -1 and 1, any value <1 shows dissociation and value >1 shows association.

[rasbt]

That's a good point, thanks for suggesting that! Currently, I don't have the capacity to code it up, but I would welcome PRs!

[zuari1993]

I went throught the test cases, and they are not equipped to handle a new metric. They should be modified as well.

I am interested and can take this up.

[rasbt]

If you have the time to contribute this, that'd be nice!