ggplotに複数レベルのx軸を追加する方法

Question

variable <-  c("PM10","SO2","NO","NO2","PM10","SO2","NO","NO2","PM10","SO2","NO","NO2","PM10","SO2","NO","NO2","PM10","SO2","NO","NO2","PM10","SO2","NO","NO2") 
sex <- c("male","male","male","male","female","female","female","female", 
    "male","male","male","male","female","female","female","female", 
    "male","male","male","male","female","female","female","female") 
exposureperiod <- c("P1","P1","P1","P1","P1","P1","P1","P1", 
       "P2","P2","P2","P2","P2","P2","P2","P2", 
       "P3","P3","P3","P3","P3","P3","P3","P3") 

set.seed(100) 
coef <- runif(24, -2, 2) 
coef_lb <- coef - 0.3 
coef_ub <- coef + 0.3 

df <- data.frame(variable,sex,exposureperiod,coef,coef_lb,coef_ub) 

df$variable <- factor(df$variable,levels=c("PM10","SO2","NO","NO2")) 
levels(df$variable) <- c("PM[10]","SO[2]", "NO", "NO[2]") 

df$exposureperiod <- factor(df$exposureperiod,levels=c("P1","P2","P3")) 
df$sex <- factor(df$sex,levels=c("male","female")) 

df <- df[order(df$variable,df$sex),] 

df$aux <- c(1,2,3, 
     5,6,7, 
     11,12,13, 
     15,16,17, 
     21,22,23, 
     25,26,27, 
     31,32,33, 
     35,36,37) 

library(ggplot2) 

plot <- ggplot(data = df, aes(x = aux, y = coef)) + 
    geom_pointrange(aes(ymin=coef_lb,ymax=coef_ub),shape="none") + 
    geom_point(aes(shape = exposureperiod)) + 
    scale_shape_discrete(name ="Exposure period", 
        breaks=c("P1", "P2","P3"), 
        labels=c("P1","P2","P3")) + 
    scale_x_continuous("Sex and Pollutant",breaks=c(2,6,12,16,22,26,32,36), 
       labels=c("Boys","Girls","Boys","Girls","Boys","Girls","Boys","Girls")) + 
    scale_y_continuous("Mean Difference in Tanner Stage", 
       limits=c(-3, 3), 
       breaks=round(seq(-3, 3, by = 0.5),1)) + 
    geom_hline(yintercept=0,alpha=1,linetype="dashed") + 
    theme(axis.text.x = element_text()) + 
    theme_bw(base_size = 16,base_family="Arial") + 
    theme(legend.text.align = 0, 
    legend.title = element_text(face="plain"), 
    legend.key = element_blank(), 
    legend.position = "bottom") + 
    guides(shape= guide_legend(nrow = 3,byrow = TRUE)) + 
    theme(text = element_text(colour = "black",face="plain"), 
    axis.title.y = element_text(face="plain"), 
    axis.title.x = element_text(face="plain"), 
    axis.text.x = element_text(face="plain",hjust = 0), 
    axis.text.y = element_text(face="plain")) + 
    theme(panel.background = element_blank(), 
    panel.grid.major = element_blank(), 
    panel.grid.minor = element_blank(), 
    panel.border = element_blank(), 
    axis.line = element_line(colour = "black"))+ 
    theme(axis.ticks = element_line(size = 1)) 

plot 

上記のスクリプトでは、次のようなグラフが得られました。

しかし、私は下のグラフのように、PM10、SO2、NO、NO2とを示しており、x軸の別のレベルを追加します。 （説明のために、私はこれらの汚染物質を手動で追加しました。）もちろん、x軸のタイトルと凡例はそれに応じて下に移動する必要があります。

私は以前にファセットを使用しましたが、ファセットによって生成される汚染物質の間のギャップを避けたいと思います。

ありがとうございます。

Answer 1

あなたは、私が汚染物質によって、ファセットにお勧めしたい

plot <- plot + facet_wrap(~variable)