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我们通常会希望使用ggplot2创建横向、纵向并列图，方便同时对比查看数据的不同方面特性。我们可以使用patchwork包很容易实现。

加载包

#install ggplot2 and patchwork packages
install.packages('ggplot2')
install.packages('patchwork')#load the packages 
library(ggplot2)
library(patchwork)

本文我们展示几个示例教你使用这些包创建多个并列图。

两个并列图

下面代码展示如何创建两个并列图，使用R内置的iris数据集：

#create box plot
plot1 <- ggplot(iris, aes(x = Species, y = Sepal.Length)) +geom_boxplot()#create density plot
plot2 <- ggplot(iris, aes(x = Sepal.Length, fill = Species)) +geom_density(alpha = 0.8)#display plots side by side
plot1 + plot2 

三个并列图

下面代码展示如何创建三个并列图：

#create box plot
plot1 <- ggplot(iris, aes(x = Species, y = Sepal.Length)) +geom_boxplot()#create density plot
plot2 <- ggplot(iris, aes(x = Sepal.Length, fill = Species)) +geom_density(alpha = 0.7)#create scatterplot 
plot3 <- ggplot(iris, aes(x = Sepal.Length, y = Sepal.Width)) +geom_point(aes(colour=factor(Species), shape=factor(Species)))#display three plots side by side
plot1 + plot2 + plot3

两个垂直排列图

下面代码展示如何创建两个垂直排列图：

#create box plot
plot1 <- ggplot(iris, aes(x = Species, y = Sepal.Length)) +geom_boxplot()#create density plot
plot2 <- ggplot(iris, aes(x = Sepal.Length, fill = Species)) +geom_density(alpha = 0.7)#display plots stacked on top of each other
plot1 / plot2 

组合排列

下面展示上面一行一个图，下面一行并列展示两个图：

#create box plot
plot1 <- ggplot(iris, aes(x = Species, y = Sepal.Length)) +geom_boxplot()#create density plot
plot2 <- ggplot(iris, aes(x = Sepal.Length, fill = Species)) +geom_density(alpha = 0.7)#create scatterplot 
plot3 <- ggplot(iris, aes(x = Sepal.Length, y = Sepal.Width)) +geom_point(aes(colour=factor(Species), shape=factor(Species)))#display plots stacked on top of each other
plot1 / (plot2 + plot3)

给组合图增加标题、子标题、题注

plot_annotation函数可以实现对组合图添加标题、子标题、题注等，下面代码展示如何实现：

#create box plot
plot1 <- ggplot(iris, aes(x = Species, y = Sepal.Length)) +geom_boxplot() +ggtitle('Boxplot')#create density plot
plot2 <- ggplot(iris, aes(x = Sepal.Length, fill = Species)) +geom_density(alpha = 0.7) +ggtitle('Density Plot')#display plots side by side with title, subtitle, and captions
patchwork <- plot1 + plot2 patchwork + plot_annotation(title = 'This is a title',subtitle = 'This is a subtitle that describes more information about the plots',caption = 'This is a caption',theme = theme(plot.title = element_text(size = 19))
)