I am looking for what you might see as the equivalent of custom metrics in GA. The custom variables in Piwik seem more akin to custom dimensions in GA. But I would need an additional field (which would only be integers) that could be summed/averaged/other simple math function on a list of numbers.
An offhand example would be tracking the size of a download the user has completed on a page visit. And I would like to query the total size that user has downloaded. Is that possible with Piwik?
Also I would only be using the core Tracking/Reporting API themselves. I’ve looked over them, but didn’t notice anything similar to what I’m talking about.