如何在patchwork的wrap_plots中仅保留散点图的图例？

当使用patchwork合并多个ggplot2图形（包括散点图和直方图）时，默认会保留所有图例，需要仅保留散点图的图例且自动居中，无需手动调整尺寸适配自动化流程。

原复现代码：

library(ggplot2)
library(patchwork)

plot_histogram <- function() {
    plot_data <- ggplot(mtcars, aes(x = mpg, fill = factor(am))) +
        geom_histogram(binwidth = 2, color = "black") +
        labs(title = "Histo",
             x = "Miles/gallon",
             y = "nb cars",
             fill = "Transmission") +
        scale_fill_manual(values = c("skyblue", "salmon"), 
                          labels = c("Auto", "Man")) +
        theme_minimal() +
        theme(legend.position = "bottom")
    
    return(plot_data)
}

plot_scatter <- function() {
    plot_data <- ggplot(mtcars, aes(x = mpg, y = wt, color = factor(cyl))) +
        geom_point(size = 3) +
        labs(title = "Scatterplot",
             x = "Miles/gallon",
             y = "weight",
             color = "Cyl") +
        theme_minimal() +
        theme(legend.position = "bottom")
    
    return(plot_data)
}

scatter_plot_left <- plot_scatter()
scatter_plot_right <- plot_scatter()
histogram_plot <- plot_histogram()

combined_plots <- wrap_plots(scatter_plot_left + scatter_plot_right,
                             histogram_plot,
                             nrow = 1,
                             widths = c(3, 1)) +
    plot_layout(guides = 'collect') &
    theme(legend.position = "bottom")

combined_plots

解决方案 #

方法1：修改直方图生成函数，直接移除其图例

在plot_histogram函数中设置隐藏图例，合并时就不会收集到它的图例：

plot_histogram <- function() {
    plot_data <- ggplot(mtcars, aes(x = mpg, fill = factor(am))) +
        geom_histogram(binwidth = 2, color = "black") +
        labs(title = "Histo",
             x = "Miles/gallon",
             y = "nb cars",
             fill = "Transmission") +
        scale_fill_manual(values = c("skyblue", "salmon"), 
                          labels = c("Auto", "Man")) +
        theme_minimal() +
        theme(legend.position = "none")  # 隐藏直方图图例
    
    return(plot_data)
}

保持原合并代码不变，plot_layout(guides='collect')会自动收集散点图的图例，并将其居中放置在整个组合图底部，无需手动调整。

方法2：不修改原函数，合并时临时移除直方图的图例

如果不想改动原函数，可以在合并前对直方图对象临时修改，隐藏其图例：

scatter_plot_left <- plot_scatter()
scatter_plot_right <- plot_scatter()
# 临时隐藏直方图的图例
histogram_plot <- plot_histogram() + theme(legend.position = "none")

combined_plots <- wrap_plots(scatter_plot_left + scatter_plot_right,
                             histogram_plot,
                             nrow = 1,
                             widths = c(3, 1)) +
    plot_layout(guides = 'collect') &
    theme(legend.position = "bottom")

combined_plots

原理说明 #

• 通过theme(legend.position = "none")移除直方图的图例后，plot_layout(guides='collect')只会收集散点图的图例。
• patchwork会自动将收集到的图例居中对齐在整个组合图底部，尺寸自适应，完全适配自动化生成流程。

内容的提问来源于stack exchange，提问作者NoNameBoyy