R Plotly堆积条形图问题

Question

我正在使用plotly来创建类似下面的堆积条形图

df <- data.frame(
  var1 = c("NY", "NY", "NY", "SFO", "SFO", "SFO"),
  var2 =  c("Low", "Medium", "High", "Low", "Medium", "High"),
  value = c(10,15,20,10,20,25)
)
df$var2 <- factor(df$var2, levels = c("Low","Medium","High"))

# sort the factor table
df <- arrange(df, var2)

col <- list(
  color = ifelse(
    df$var2 == "Low",
    "steelblue",
    ifelse(
      df$var2 == "Medium",
      "darkorange",
      "olivedrab"
    )
  ))

# Plot
plot_ly(
  df,
  x = ~ var1,
  y = ~ value,
  color = ~ var2,
  marker = col,
  type = "bar"
) %>% layout(barmode = "stack")

我面临两个问题：首先是图例没有正确显示（见图片）。

其次是因为我拥有的是动态表，所以var1和var2中只有一个值，所以它就像

df <- data.frame(var1 = c("NY"),
                 var2 =  c("Low"),
                 value = c(10))
df$var2 <- factor(df$var2, levels = c("Low", "Medium", "High"))

# sort the factor table
df <- arrange(df, var2)

col <- list(color = ifelse(
  df$var2 == "Low",
  "steelblue",
  ifelse(df$var2 == "Medium",
         "darkorange",
         "olivedrab")
))

# Plot
plot_ly(
  df,
  x = ~ var1,
  y = ~ value,
  color = ~ var2,
  marker = col,
  type = "bar"
) %>% layout(barmode = "stack")

在这种情况下，图表不会显示。如果我在var1中有2个值 或者在var2中，图表仍然显示但不显示。有人能告诉我如何处理这个问题吗？

感谢， Manoj