匹配 R 中的 Y 双轴值答案

【问题标题】：Match Y dual axis values in R匹配 R 中的 Y 双轴值
【发布时间】：2022-11-27 05:58:45
【问题描述】：

我知道不鼓励在单个图上绘制 2 个单独的 y 轴，这可能会造成混淆和误导。

有没有办法匹配 Y 轴的值？例如找到一种方法在图表中移动右 Y 轴数据（？）例如，我希望左侧 Y 轴中的 40 与右侧 Y 轴中的 -1 匹配，因为这两个值对应于干旱条件类别的开始。

样本：

structure(list(Time = structure(c(9862, 9893, 9921, 9952, 9982, 
10013, 10043, 10074, 10105, 10135, 10166, 10196, 10227, 10258, 
10286, 10317, 10347, 10378, 10408, 10439), class = "Date"), Year = c(1997, 
1997, 1997, 1997, 1997, 1997, 1997, 1997, 1997, 1997, 1997, 1997, 
1998, 1998, 1998, 1998, 1998, 1998, 1998, 1998), VCI = c(48.7488482440362, 
51.8662335250972, 54.4212125411374, 61.7338808190779, 63.9870065731148, 
61.3375357670741, 62.6197335631611, 63.0950799644754, 61.6276947895731, 
61.1298324406371, 64.4422427513358, 60.3823204404222, 60.5883337239537, 
61.8918834440238, 59.1304135098709, 62.1668350554954, 61.9352586665065, 
55.75795384214, 50.3371363875305, 52.5748728440737), TCI = c(53.7071192239754, 
53.6178820221828, 57.7831310561669, 57.3996088686986, 49.8613200877384, 
54.9673093834738, 42.4962626269047, 33.542249807155, 36.9526033996693, 
46.0464770178552, 49.5240246297537, 49.6298842520857, 47.9889200846868, 
40.3862301499032, 36.8605803231892, 38.8799158911488, 39.0120455451407, 
45.9071510330717, 55.8730250709158, 60.4339176493461), SPEI = c(0.385767341805337, 
-0.240467091114443, 0.218601001011986, 0.392296211626228, -0.0041472667529566, 
0.36089672045203, -0.415596363086708, -0.694577131096395, -0.53422184521265, 
0.372791671097943, 0.0714646484375678, 0.100567550879492, 0.484279813014397, 
-0.478876226785371, -0.591222448288627, -0.473201395390211, -0.347352514594038, 
-0.432571106796894, -0.259775061906046, 0.114961224539346)), row.names = c(NA, 
20L), class = "data.frame")

这是代码：

## Plot first set of data and draw its axis
par(mar = c(5, 5, 4, 4))
#VCI index
plot(variables$Time, variables$VCI, pch=20, cex=.9, axes=FALSE, ylim=c(0,100), xlab="", ylab="", 
     type="l",col="Aquamarine3", main="Temporal trend - drought indices, growing season")
axis(2, ylim=c(0,100),col="black",las=1)  ## las=1 makes horizontal labels
mtext("VCI and TCI",side=2,line=2.5)
box()
abline(h = 40, col = "black", lty = "dotted", lwd= 2)


## Allow a second plot on the same graph
par(new=TRUE)

#TCI index
plot(variables$Time, variables$TCI, pch=21, cex = 1.2, axes=FALSE, ylim=c(0,100), xlab="", ylab="", 
     type="l",col="Chocolate2", main="Temporal trend - drought indices, growing season")
axis(2, ylim=c(0,100),col="grey",las=1)  ## las=1 makes horizontal labels
mtext("VCI and TCI",side=2,line=2.5)
box()


## Allow a second plot on the same graph
par(new=TRUE)

## Plot the second plot and put axis scale on right
plot(variables$Time, variables$SPEI, pch=15, cex=.4, xlab="", ylab="", ylim=c(-2.5,2.5), 
     axes=FALSE, type="l", col="darkorchid3")
abline(h = -1.5, col = "black", lty = "dashed", lwd= 2)

## a little farther out (line=4) to make room for labels
mtext("SPEI",side=4,line=2.5)
axis(4, ylim=c(-2.5, 2.5), col="black",col.axis="black",las=1)

par(new=TRUE)
## Draw the time axis
axis(1, spei.df$Time, format(spei.df$Time, "%Y"), 20)
mtext("Time",side=1,col="black",line=2.5)  

## Add Legend
legend("topleft",legend=c("VCI","TCI", "SPEI"),
       text.col=c("black","black", "black"), lty=1, lwd=2, col=c("Aquamarine3","Chocolate2", "darkorchid3"))

【问题讨论】：

您可以使用线性插值来计算第二轴的 y 限制。
我不明白这与我的需要有什么关系？

标签： r plot graph time-series

【解决方案1】：

我不确定你是如何在 base R 中做到这一点的，但你可以通过一些数学和 ggplot2 的反复试验来对齐第二个轴

library(tidyverse)

dat |>
  mutate(SPEI = (SPEI+(25/15))*15)|>
  pivot_longer(VCI:SPEI) |>
  mutate(name = factor(name, levels = c("VCI", "TCI", "SPEI"))) |>
  ggplot(aes(Time, value, color = name))+
  geom_line()+
  geom_hline(linetype = "dotted", yintercept = 40)+ 
  geom_hline(linetype = "dashed", yintercept = 2.5)+
  scale_color_manual(values = c("Aquamarine3", "Chocolate2", "darkorchid3"))+
  scale_y_continuous(name = "VCI and TCI", 
                     breaks = seq(0, 100, by = 20),
                     limits = c(0, 100),
                     sec.axis = sec_axis(trans = ~(./15)-(25/15), name = "SPEI", 
                                         breaks = seq(-2,5, by = 1)))+
  ggtitle("Temporal trend - drought indices, growing season")+
  labs(color = "")+
  theme(panel.background = element_blank(),
        panel.border = element_rect(fill = NA, color = "black"),
        legend.key = element_blank(),
        legend.box.background = element_rect(fill = NA, color = "black"),
        legend.position = c(0.07,0.87),
        legend.title = element_blank())

【讨论】：