如何为R语言中2×2布局的图形添加行标题

我创建了一个2×2布局的图形，其中列代表两个不同变量，行代表两个不同地点。请问如何为这两行添加对应的地点名称？

示例代码：

library(biwavelet)

par(mfrow = c(2,2),
    oma = c(3,3,0,0) + 0.1,
    mar = c(1,1,1,1) + 0.1)

dat <- as.data.frame(matrix(nrow = 500, ncol = 2))

dat[1] <- seq(1,500)
dat[2] <- sin(dat[1])

# top-left figure
plot(wt(dat),
     xaxt = 'n',
     xlab = "",
     cex.axis = 1.5,
     cex.lab = 1.5)
axis(1, at = seq(0, 500, by = 100), cex.axis = 0.1, col.axis = 'NA')
title("Variable 1", line = 0.1, cex.main = 1.5)

# top-right figure
dat[2] <- sin(dat[1]*.5)
plot(wt(dat),
     xaxt = 'n',
     col.axis = 'NA',
     xlab = "",
     ylab = "")
axis(1, at = seq(0, 500, by = 100), cex.axis = 0.1, col.axis = 'NA')
title("Variable 2", line = 0.1, cex.main = 1.5)

# bottom-left figure
dat[2] <- sin(dat[1]*.25)
plot(wt(dat),
     cex.axis = 1.5)

# bottom-right figure
dat[2] <- sin(dat[1]*.125)
plot(wt(dat),
     col.axis = 'NA',
     ylab = "",
     xlab = "")
axis(1, at = seq(0, 500, by = 100), cex.axis = 1.5)

title(xlab = "Time (hours)",
      ylab = "Period",
      outer = TRUE,
      line = 1.5,
      cex.lab = 1.5)

理想效果：

可以通过调整图形外边界宽度，再用mtext()函数在布局左侧添加地点名称，具体操作如下：

1. 先修改全局绘图参数，扩大左侧外边界（oma）的宽度，避免地点名称被遮挡：
   将原代码中的par(mfrow = c(2,2), oma = c(3,3,0,0) + 0.1)替换为：

   par(mfrow = c(2,2),
       oma = c(3,6,0,0) + 0.1,  # 增大左侧外边界空间
       mar = c(1,1,1,1) + 0.1)
   

2. 在所有绘图完成后，添加两行的地点名称：
   使用mtext()指定左侧（side=2）、使用外边界（outer=TRUE），并通过at参数定位到对应行的垂直中心位置：

   # 添加地点名称，可根据显示效果微调at参数值
   mtext("地点A", side = 2, outer = TRUE, line = 3, cex = 1.5, las = 1)
   mtext("地点B", side = 2, outer = TRUE, line = 3, at = 0.25, cex = 1.5, las = 1)
   

完整修改后的代码：

library(biwavelet)

par(mfrow = c(2,2),
    oma = c(3,6,0,0) + 0.1,  # 调整左侧外边界宽度
    mar = c(1,1,1,1) + 0.1)

dat <- as.data.frame(matrix(nrow = 500, ncol = 2))

dat[1] <- seq(1,500)
dat[2] <- sin(dat[1])

# top-left figure
plot(wt(dat),
     xaxt = 'n',
     xlab = "",
     cex.axis = 1.5,
     cex.lab = 1.5)
axis(1, at = seq(0, 500, by = 100), cex.axis = 0.1, col.axis = 'NA')
title("Variable 1", line = 0.1, cex.main = 1.5)

# top-right figure
dat[2] <- sin(dat[1]*.5)
plot(wt(dat),
     xaxt = 'n',
     col.axis = 'NA',
     xlab = "",
     ylab = "")
axis(1, at = seq(0, 500, by = 100), cex.axis = 0.1, col.axis = 'NA')
title("Variable 2", line = 0.1, cex.main = 1.5)

# bottom-left figure
dat[2] <- sin(dat[1]*.25)
plot(wt(dat),
     cex.axis = 1.5)

# bottom-right figure
dat[2] <- sin(dat[1]*.125)
plot(wt(dat),
     col.axis = 'NA',
     ylab = "",
     xlab = "")
axis(1, at = seq(0, 500, by = 100), cex.axis = 1.5)

title(xlab = "Time (hours)",
      ylab = "Period",
      outer = TRUE,
      line = 1.5,
      cex.lab = 1.5)

# 添加两行的地点名称
mtext("地点A", side = 2, outer = TRUE, line = 3, cex = 1.5, las = 1)
mtext("地点B", side = 2, outer = TRUE, line = 3, at = 0.25, cex = 1.5, las = 1)

这样就能在布局左侧对应行的位置添加地点名称，和理想效果匹配。

内容的提问来源于stack exchange，提问作者tassones