ggplotly() is unable to merge legend entries across layers

Thanks for an amazing package! The mapping between plotly and ggplot is particularly impressive and very powerful!

However, ggplotly fails to reproduce the appropriate legends generated by ggplot in non-trivial facet_wrap cases. After discussion on stackoverflow some of this behavior appears to be a bug.

Consider the following minimal reprex:

library(plotly)
library(ggplot2)

p <- mpg %>% 
  ggplot(aes(year)) +
  geom_ribbon(aes(ymin=cty, ymax=hwy, fill = manufacturer), alpha=0.2) + 
  geom_line(aes(y = hwy, col=manufacturer))  +
  facet_wrap(~class)
p
plotly::ggplotly(p)

Note that (a) we get too many plotly legend entries, duplicating the legend for each facet, due to legendgroup not being correctly handled. Also note (b) the legends we do and don't get depend on the order (do we do geom_ribbon first or geom_line first). The bug does not appear if we have only one geom, and the missing legends continue as we add more geoms.

Perhaps not related -- but the interactive zoom options in faceted plots are not entirely intuitive either, i.e. it's not possible to zoom the whole window on a single facet plot. (Perhaps the take home is that it might be better to render facet plots as more independent objects in plotly)?

从使用 geom_ribbon、geom_line 和 facet_wrap(~class) 的最小 ggplotly() reprex 开始，然后检查 legendgroup 在各图层和分面之间的处理方式。将转换后的图例与 ggplot2 预期的图例进行比较；无论 geom 的顺序如何，都没有重复或缺失的条目，同时保留分面行为，即视为完成。