如何基于Plotly的subplot实现各子图带独立图例的分面图？

我之前用htmltools结合Plotly生成了分面条形图，代码如下：

library(plotly)
library(htmltools)

legend <- list(orientation = "v", y = 1, x = .85)

fig1 <- plot_ly(
  x = c("orangutans1", "orangutans", "monkeys"),
  y = c(10, 1, 3),
  name = "SF Zoo",
  type = "bar", marker = list(color = "blue"),
  legendgroup = "1"
) |>
  layout(showlegend = TRUE, legend = legend, 
         title = 'Title 1')

fig2 <- plot_ly(
  x = c("giraffes", "orangutans", "monkeys"),
  y = c(10, 84, 32),
  name = "SF Zoo",
  type = "bar", marker = list(color = "royalblue"),
  legendgroup = "2"
) |>
  layout(showlegend = TRUE, legend = legend,title = 'Title 2')

fig3 <- plot_ly(
  x = c("giraffes", "orangutans", "monkeys"),
  y = c(5, 14, 27),
  name = "SF Zoo",
  type = "bar", marker = list(color = "green")
) |>
  layout(showlegend = TRUE, legend = legend,title = 'Title 3')

fig4 <- plot_ly(
  x = c("giraffes", "orangutans", "monkeys"),
  y = c(22, 24, 67),
  name = "SF Zoo",
  type = "bar", marker = list(color = "black")
) |>
  layout(showlegend = TRUE, legend = legend,title = 'Title 4')

htmltools::div(
  crosstalk::bscols(
    fig1, fig2
  ),
  crosstalk::bscols(
    fig3, fig4
  )
) |>
  htmltools::browsable()

这种方式生成的是四个独立图表，虽然每个子图配有独立图例，但无法正常导出为PDF格式。现在需要改用Plotly的subplot功能，实现带独立图例的分面图，同时支持PDF导出。

核心是通过subplot整合所有子图为单个Plotly对象，配合legendgroup和自定义图例位置，实现每个子图的独立图例，具体代码如下：

library(plotly)

# 定义统一的图例布局（可按需调整位置）
get_legend_layout <- function() {
  list(orientation = "v", y = 0.95, x = 0.8, 
       tracegroupgap = 0, bgcolor = "rgba(255,255,255,0.8)")
}

# 创建子图1
fig1 <- plot_ly(
  x = c("orangutans1", "orangutans", "monkeys"),
  y = c(10, 1, 3),
  name = "SF Zoo",
  type = "bar", marker = list(color = "blue"),
  legendgroup = "fig1"  # 唯一图例组标识
) |>
  layout(
    title = list(text = 'Title 1', x = 0.05),
    showlegend = TRUE,
    legend = get_legend_layout(),
    margin = list(l = 50, r = 80, t = 40, b = 40)  # 预留图例空间
  )

# 创建子图2
fig2 <- plot_ly(
  x = c("giraffes", "orangutans", "monkeys"),
  y = c(10, 84, 32),
  name = "SF Zoo",
  type = "bar", marker = list(color = "royalblue"),
  legendgroup = "fig2"
) |>
  layout(
    title = list(text = 'Title 2', x = 0.05),
    showlegend = TRUE,
    legend = get_legend_layout(),
    margin = list(l = 50, r = 80, t = 40, b = 40)
  )

# 创建子图3
fig3 <- plot_ly(
  x = c("giraffes", "orangutans", "monkeys"),
  y = c(5, 14, 27),
  name = "SF Zoo",
  type = "bar", marker = list(color = "green"),
  legendgroup = "fig3"
) |>
  layout(
    title = list(text = 'Title 3', x = 0.05),
    showlegend = TRUE,
    legend = get_legend_layout(),
    margin = list(l = 50, r = 80, t = 40, b = 40)
  )

# 创建子图4
fig4 <- plot_ly(
  x = c("giraffes", "orangutans", "monkeys"),
  y = c(22, 24, 67),
  name = "SF Zoo",
  type = "bar", marker = list(color = "black"),
  legendgroup = "fig4"
) |>
  layout(
    title = list(text = 'Title 4', x = 0.05),
    showlegend = TRUE,
    legend = get_legend_layout(),
    margin = list(l = 50, r = 80, t = 40, b = 40)
  )

# 组合为2行2列的子图
combined_fig <- subplot(
  fig1, fig2,
  fig3, fig4,
  nrows = 2,
  shareX = FALSE,  # 按需设置是否共享X轴
  shareY = FALSE,  # 按需设置是否共享Y轴
  margin = 0.08  # 子图间间距
) |>
  layout(title = list(text = "分面条形图（带独立图例）", x = 0.5))

# 查看交互式图表
combined_fig

# 导出为PDF（需提前安装orca工具）
# plotly::orca(combined_fig, "subplot_with_legends.pdf")

关键说明 #

• 图例独立性：给每个子图设置唯一legendgroup，确保图例互不干扰，各自独立显示
• 图例位置控制：通过legend参数的x/y坐标，将图例固定在子图内部右侧，避免子图重叠
• 间距调整：subplot的margin控制子图间距离，每个子图的layout$margin预留图例空间
• PDF导出：生成的combined_fig是单个Plotly对象，可直接用orca()命令导出为PDF，或在RStudio中通过「Export」按钮导出

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