Show normalized visit stats in RowEvolution #3729

The row evolution feature would be much more useful if one could switch to normalized visitor data. The perfect example is the comparison of browser version over time, which by now is not doable using Piwik alone

All we would need to do is to divide the absolute number of visits by the total number of visits for each time step, and change the y-axis to percentages.

see related (Show % for all metrics in all piwik reports) #1816

+1 on that - it seems to me the row evolution is useful only for the number of visitors and all other graphs are skewed over that distribution, making this new feature mainly unusable for any other graph...

so what would be a good way to implement this feature?

the maths behind this are very easy, but I have no idea where would be the best place to insert it.

maybe it would make sense to add report normalization to the core at a lower level, so that every report (except for nb_visits) can be normalized (e.g. by adding &normalize=1 to the API request). Then row evolution could simply forward the parameter.

what do you think about it?

(Multi) Row Evolution graphs could show both numbers and % value, so we have 1 graph fit-them-all. eg. the left Y axis could show numbers and Y axis on the right show the percentage value, and tooltip could show both Metric+Normalized values, would it work?