No way to make legend order exactly match bar order in relative stacked bar plot

Sometimes we want to plot negative values below x axis in a stacked bar plot. This can be done with barmode as "relative".

Further, I want to make the legend order exactly match the bar order in plot. However the positive bars stack from middle to top, negative bars stack from middle to down, thus no matter how I arrange the variable levels, there is no way to make the legend order exactly match bar order.

library(plotly)
library(data.table)

set.seed(42)
dt_test <- data.table(x = rep(1:5, each = 6), variable = rep(letters[1:6], 5), value = sample(10:40, 30))
dt_test[variable %in% letters[3:5], value := -value]

dt_test[, variable := factor(variable, levels = c("c", "d", "e", "a", "b", "f"))]

plot_ly(dt_test) %>% 
  add_bars(x = ~x, y = ~value, color = ~variable) %>%
  layout(barmode = 'relative', legend = list(traceorder = "reversed"))

I'm not sure how this can be done, unless we

• change the stack order in negative part as bottom up
• or can arrange legend order freely without changing bar stack order

首先使用 plot_ly()、add_bars()、barmode = "relative" 和当前的图例设置重现所提供的 R 示例。调查是否可以支持负堆叠和正堆叠的所需行为；当图例顺序与可见的条形顺序完全一致，或已记录该限制和所选择的排序行为时，即视为完成。