R语言plotly绘制组合图时如何为cost图例项添加黑色边框

我有3个数值变量，使用plot_ly绘制组合图：其中sale和share列以分组柱状形式可视化，cost列以红色折线展示。现在需要自定义调整图例，为图例中的cost标识添加黑色边框，效果见预期输出。

df <- data.frame (model  = c("A", "B", "C","D","E","F"),
                  share = c(12,20,15,9,60,20),
                  sale = c(16,25,18,14,67,28),
                  cost = c(14,19,28,24,57,28))

# 按cost列排序设置model因子水平
df$model <- factor(df$model, levels = arrange(df, desc(df$cost))$model)

library(tidyverse)

df_long <- df %>% 
  pivot_longer(
    cols = -model
  ) 


df_long %>% 
  filter(name != "cost") %>% 
  plot_ly(x = ~model, y = ~value, color = ~name, type = "bar", 
          customdata = ~name,  colors = c("blue", "gray"),
          hovertemplate = paste0("Model: %{x}<br>Value: %{y}<br>",
                                 "Name: %{customdata}<extra></extra>")) %>%
  add_lines(inherit = F, data = df, x = ~model, 
            y = ~cost, color = I("red"),
            name = "cost",
            hovertemplate = paste0("Model: %{x}<br>Value: %{y}<br>",
                                   "Name: cost<extra></extra>")) %>% 
  add_annotations(data = df, x = ~model, y = ~cost, text = ~cost,
                  bgcolor = "white", bordercolor = "black", 
                  xshift = 15, yshift = 15, showarrow = F) %>% 
  layout(barmode = "group")

• 当前运行输出：
  
• 预期输出效果：
  

只需要在add_lines()层中添加配置，单独为cost对应的图例标记设置黑色边框即可，不需要修改图中折线的显示样式。

推荐方案（高版本plotly适用） #

直接使用legendmarker参数单独控制图例标记样式，不会对图中折线产生任何影响，修改后的add_lines()部分代码如下：

add_lines(inherit = F, data = df, x = ~model, 
          y = ~cost, color = I("red"),
          name = "cost",
          # 为图例中的cost标识添加1px宽的黑色边框
          legendmarker = list(bordercolor = "black", borderwidth = 1),
          hovertemplate = paste0("Model: %{x}<br>Value: %{y}<br>",
                                 "Name: cost<extra></extra>"))

低版本兼容方案 #

如果使用的plotly版本较低不支持legendmarker参数，可以给折线层添加极小尺寸的标记，仅让标记的黑色边框在图例中显示，不会影响折线本身的展示效果，代码如下：

add_lines(inherit = F, data = df, x = ~model, 
          y = ~cost, color = I("red"),
          name = "cost",
          mode = "lines+markers",
          marker = list(
            color = "red",
            # 标记设置黑色边框
            line = list(color = "black", width = 1),
            # 标记大小设为0.1，图上几乎不可见，仅在图例中生效
            size = 0.1
          ),
          hovertemplate = paste0("Model: %{x}<br>Value: %{y}<br>",
                                 "Name: cost<extra></extra>"))

把对应部分替换到原代码中，运行即可得到预期的图例效果。

内容的提问来源于stack exchange，提问作者user18937485