Grouped boxplot data not centred on xaxis ticks, looses boxgap argument, and wont resize with subplots

Hi @cpsievert!

Here after your Shiny webinar, great stuff!

I'm having issues with the boxplot data aligning with x-axis tick marks in subplots. Please see below:

library (data.table)
library (stringr)
library (plotly)
# some setup:
get_plot_title = function(this.plot.title, y.pos = 1, y.shift = 0){
  list(text = sprintf ("<b>%s</b>", this.plot.title), yshift = y.shift
       , xref = "paper", yref = "paper", yanchor = "center", xanchor = "center", align = "center"
       , x = 0.5, y = y.pos, showarrow = FALSE, font = list (size = 16, family = "Arial")
  )} 

generate_panel = function(dat, trace.name){
  my.plot = 
    plot_ly(dat, type = "box"
            , x= ~get(x_var), y= ~get(y_var), color = ~get(color_var)
            , whiskerwidth = 0.1
            , boxpoints = F
    )   %>% 
    layout(boxmode = "group", boxgroupgap = 0.1, boxgap = 0.15
           , plot_bgcolor = "#F5F5F5"
           , annotations = get_plot_title(trace.name, y.shift = 20)
           , xaxis = list(title = "", tickfont = list(size = 14, family = "Arial")
                          , tickmode = "linear", ticks = "outside")
           , yaxis = list(title = sprintf("<b>%s</b>", y_var), titlefont = list (size = 16, family = "Arial"))
           ) 
  my.plot #return
}

x_var = "cut"
y_var = "price"
color_var = "color" 
X_panel_var = "clarity"
test.dat = ggplot2::diamonds %>% setDT

Without subplots, everything looks great:

generate_panel(test.dat, trace.name = "all")

Adding two horizontal subplots:

test.dat[, get(X_panel_var) %>% levels][1:2] %>% 
  lapply(function(this.panel.var){
    generate_panel(dat = test.dat[this.panel.var, on = X_panel_var], trace.name = this.panel.var)
  }) %>% 
  subplot(shareY = T, shareX = F, titleX = F, nrows = 1, which_layout = 1, margin = 0.01)

Boxplot groups shift off the centre of the xaxis ticks, and the boxgap argument becomes irrelevant:

Enlarging this plot does not work at all (cuts off the data at the original subplot width and height, yikes!):

Interestingly, with 3 horizontal subplots, the middle plot data is centered around ticks, but the outer plots are even further away (and the boxgaps are worse):

test.dat[, get(X_panel_var) %>% levels][1:3] %>% 
  lapply(function(this.panel.var){
    generate_panel(dat = test.dat[this.panel.var, on = X_panel_var], trace.name = this.panel.var)
  }) %>% 
  subplot(shareY = T, shareX = F, titleX = F, nrows = 1, which_layout = 1, margin = 0.01) 

Just wondering if you have any ideas / suggestions?

Thank you!

Reproduce the supplied R diamonds example using generate_panel and subplot with two and three horizontal panels. Investigate the subplot boxplot layout and resizing entry points first. Done means grouped boxes remain centred on x-axis ticks, boxgap is respected, and enlarged subplots display all data.