Problem when using color and size argument with observation with only one value

[BastienFR]

I'm trying to make a plot with plotly that have colors representing some class (factor ff in my example) and the size representing the population size (column ss in my example). I've posted on stackoverflow first here which got me further but I couldn't completely fix it and I think it's a bug.

Here is a reproductive example:

set.seed(123)
dd <- data.frame(
  xx = rnorm(10),
  yy = rnorm(10),
  ff = as.factor(c("a","b","c","a","b","c","a","a","b","c")),
  ss = round(runif(10, 100,1000))
)
dd2 <- dd
dd2 <- rbind(dd2, data.frame(xx=-.5, yy=1.5, ff="d", ss=50))
dd3 <- dd2
dd3 <- rbind(dd3, data.frame(xx=.5, yy=1.5, ff="d", ss=100))

I prepare 3 data.frame. The first one (dd) is the basic one. The second one (dd2), I add only one observation with a tiny size and a unique factor. He's alone in it's class. The last one (dd3), I add a friend to the last observation from dd2. Plotting works on dd and dd3 but not dd2 (see below).

pp <- plot_ly(data = dd,
               x = ~xx,
               y = ~yy,
               size= ~ss ,
               hoverinfo = 'text', text = ~ss,
               color = ~ff)
add_markers(pp,mode = "markers",
            marker = list(sizeref = 3,
                          sizemode= "area"))
pp2 <- plot_ly(data = dd2,
               x = ~xx,
               y = ~yy,
               size= ~ss ,
               hoverinfo = 'text', text = ~ss,
               color = ~ff)
add_markers(pp2,mode = "markers",
            marker = list(sizeref = 3,
                          sizemode= "area"))

pp3 <- plot_ly(data = dd3,
               x = ~xx,
               y = ~yy,
               size= ~ss ,
               hoverinfo = 'text', text = ~ss,
               color = ~ff)
add_markers(pp3,mode = "markers",
            marker = list(sizeref = 3,
                          sizemode= "area"))

The size of observation 11 (factor d) is way bigger than it should in comparison with other class for plot 2. But as soon as we add a new observation in the same class, everything seems fix.

[cpsievert]

This is likely related to the fact that sizing rules are different in plotly.js for an array of length 1 compared a constant. I'm not sure the best way to resolve this. If I were to rewrite plotly, I would make sure it's always an array, as in #1176, but it might be too late to introduce such in breaking change.