ggplot2：将两组添加到一个方面

Question

我有一个数据框，其中包含来自两个位置的年度温度时间序列（即 Site 1 和 Site 2）。三个温度变量是：

1. Air温度
2. Water温度
3. Difference = Air - Water

   我想制作一个四面板图，其中顶行和底行分别是Site 1和Site 2，左列显示Air和Water，右列显示Difference。有没有办法使用facet_wrap()或facet_grid()来做到这一点？

   示例数据

   library(data.table)
   library(dplyr)
   library(ggplot2)
   
   set.seed(321)
   
   # Create the example air and water temperature time series
   df1 <- data.frame(matrix(ncol = 4, nrow = 365*4))
   colnames(df1)[1:4] <- c("Location","Variable", "Date", "Temperature")
   df1[1:730,1] <- "Site 1"
   df1[731:NROW(df1),1] <- "Site 2"
   df1[c(1:365,731:1095),2] <- "Air"
   df1[c(366:730,1096:NROW(df1)),2] <- "Water"
   df1$Date <- rep(seq.Date(as.Date("2021-01-01"),as.Date("2021-12-31"),"1 day"),4)
   df1$noise <- rep(runif(365),4)
   df1$t <- rep(seq(0,1*pi,,365),4)
   for (i in 1:NROW(df1)) {
     df1$Temperature[1:365] <- 20*sin(df1$t)+df1$noise*8
     df1$Temperature[365:730] <- 17*sin(df1$t)+df1$noise*2
     df1$Temperature[731:1095] <- 25*sin(df1$t)+df1$noise*6
     df1$Temperature[1096:NROW(df1)] <- 18*sin(df1$t)+df1$noise*1.5
   }
   
   # Take the difference between air and water temperature
   df1 <- df1[,1:4]
   site1 <- df1[df1$Location == 'Site 1',]
   site1 <- site1 %>%
     tidyr::pivot_wider(names_from = Variable, values_from = Temperature) %>%
     mutate(Difference = Air - Water) %>%
     tidyr::pivot_longer(cols = c('Water','Air','Difference'),
                         names_to = 'Variable',
                         values_to = 'Temperature')
   site2 <- df1[df1$Location == 'Site 2',]
   site2 <- site2 %>%
     tidyr::pivot_wider(names_from = Variable, values_from = Temperature) %>%
     mutate(Difference = Air - Water) %>%
     tidyr::pivot_longer(cols = c('Water','Air','Difference'),
                         names_to = 'Variable',
                         values_to = 'Temperature')
   
   # Recombine data from site 1 and site 2 for final dataset
   df1 <- rbind(site1,site2)
   

   这是我正在寻找的示例，但是我不想使用六面板图，而是希望同时显示 Air 和 Water，从而创建一个四面板图。

   df1 %>%
     ggplot() +
     geom_line(aes(x = Date, y = Temperature, group = Variable, color = Variable)) +
     theme_bw() +
     theme(panel.grid = element_blank(),
           text = element_text(size = 16),
           axis.text.x = element_text(size = 14, color = "black", angle = 90, vjust = 0.5, hjust = 1),
           axis.text.y = element_text(size = 14, color = "black")) +
     facet_grid(Location~Variable)
   

Answer 1

尝试创建一个将“空气”和“水”观测值分组的新变量，并将其指定到方面：

df1 %>% 
mutate(var_air_water = ## Here is the new variable
   if_else(Variable %in% c("Air", "Water"), 
   true = "Air & Water", 
   false = Variable)) %>% 
ggplot() +
geom_line(aes(x = Date, y = Temperature, group = Variable, color = Variable)) +
theme_bw() +
theme(panel.grid = element_blank(),
      text = element_text(size = 16),
      axis.text.x = element_text(size = 14, color = "black", angle = 90, vjust = 0.5, hjust = 1),
      axis.text.y = element_text(size = 14, color = "black")) +
facet_grid(Location~var_air_water)