使用2 y轴在同一图上绘制多个数据集

Question

我想将第三个数据集添加到散点图中，但它的值比其他两个数据集大几个数量级。

有没有办法在一个窗口中绘制所有三个数据集的值，在右侧y轴（轴4）上用与我用于设置3点的颜色相匹配的颜色表示数据集3的y值？这是我尝试过的：

plot(xlab = "Mb", ylab = "Pi", 
      x, yAll,          pch = 6,  cex = .5, col = "blue", type ="b" )
lines(x, yAll_filtered, pch = 18, cex = .5, col = "red",  type = "b")

这让我得到了三个数据集中的两个，然后我不知道下一步。

理想情况下，我可以用绿色绘制第3组值，并在右侧显示不同比例的y值，也是绿色。基本上，用这些参数绘制这些Y值符合

plot(x, yAll_normalized, pch = 19, cex = .5, col = "green", type = "b", 
     axis(4))

Answer 1

三个简单的选择：

pracma::plotyy graphics::axis

在绘图之前，只需缩放数据集。

如果您选择第二位，请先按常规方式绘制“左手”数据，然后拨打axis(side=4,{other setup arguments})，然后拨打lines(data3,...)

编辑 - 每个gung的有效评论，这是plotyy的帮助文件的一部分：

plotyy(x1, y1, x2, y2, gridp = TRUE, box.col = "grey",
                       type = "l", lwd = 1, lty = 1,
                       xlab = "x", ylab = "y", main = "",
                       col.y1 = "navy", col.y2 = "maroon", ...)
Arguments

x1, x2  
x-coordinates for the curves

y1, y2  
the y-values, with ordinates y1 left, y2 right.

type    
type of the curves, line or points (for both data).

这将在左侧y轴上绘制带有自动缩放的x1,y1，并在右侧y轴上绘制x2,y2。

Answer 2

（这个问题可能会更好地迁移到stats.SE，因为问题不是要调用的函数，而是了解这些事情背后的想法。）

这里的基本策略是在绘图之前缩放数据集，正如@Carl Witthoft所说。以下是它的工作原理（了解所使用的任何功能，在R控制台的提示符下输入?<function name>）：

# here I generate some example data, set.seed makes it reproducible
set.seed(33)
x <- 1:20; y0 <- 20; y1 <- 25; y2 <- 300
for(i in 2:20){
  y0 <- c(y0, y0[i-1]+rnorm(1, mean=0.25, sd=1.5))
  y1 <- c(y1, y1[i-1]+rnorm(1, mean=0,    sd=1))
  y2 <- c(y2, y2[i-1]+rnorm(1, mean=-10,  sd=5))
}
max(y0, y1)  
# [1] 35.3668
min(y0, y1)
# [1] 17.77653
# from 0 to 50 seems like a reasonable Y range for the plotting area

windows()
  plot (x, y0, pch=6,  cex=.5, col="blue", type="b", 
        xlab="Mb", ylab="Pi", ylim=c(0, 50))
  lines(x, y1, pch=18, cex=.5, col="red",  type="b")

# We need to create a new variable that will fit within this plotting area
y2new <- scale(y2)        # this makes y2 have mean 0 & sd 1
y2new <- y2new*sd(y0)     # now its sd will equal that of y0
y2new <- y2new+mean(y0)   # now its mean will also equal that of y0

  lines(x, y2new, pch=24, cex=.5, col="green", type="b")

# now y2 fits within the window, but we need an axis which must map the 
#   plotted points to the original values

summary(y0)
#    Min. 1st Qu.  Median    Mean 3rd Qu.    Max. 
#   17.78   20.64   24.34   25.62   30.25   35.37
summary(y2)
#    Min. 1st Qu.  Median    Mean 3rd Qu.    Max. 
#   125.1   178.2   222.2   220.0   266.3   300.0
sd(y0)
# [1] 5.627629
sd(y2)
#[1] 54.76167

# thus, we need an axis w/ 25.62 showing 220 instead, & where 5.63 higher
#   shows 54.76 higher instead

increments <- (mean(y0)-seq(from=0, to=50, by=10))/sd(y0)
increments
# [1]  4.5521432  2.7751960  0.9982488 -0.7786983 -2.5556455
# [6] -4.3325927
newTicks   <- mean(y2) - increments*sd(y2)
newTicks
# [1] -29.24281  68.06579 165.37438 262.68298 359.99158
# [6] 457.30017

# the bottom of the y axis in the plot is 4.55 sd's below y0's mean, 
#   thus the bottom of the new axis should be about -30, and the top of 
#   the new axis should be about 460

  axis(side=4, at=seq(0, 50, 10), labels=round(newTicks), col="green")
  legend("bottomleft", c("y0 (left axis)", "y1 (left axis)", 
         "y2 (right axis)"), pch=c(6, 18, 24), lty=1, 
         col=c("blue", "red", "green"))

所有这些都是一种痛苦。从@Carl Wittholf的回答中，我收集函数plotyy()将自动为您执行此操作（我从未使用过它），但您必须先安装（并随后加载）pracma包。