在 Lattice 的面板函数中使用 ifelse 或 if 循环不适用于 panel.xyplot

问题描述

我试图用 lattice 绘制一个图，其中点颜色和形状都根据数据中的变量而变化。当我自己设置 col 和 pch 值并且不要将 panel.xyplot 放在 ifelse 语句中时，这很好用：

#Setup
library(cluster)
library(lattice)

xyplot(V8 ~ V7,data = flower,V8_var = flower$V8,panel = function(x,y,...,V8_var,subscripts) {
         
         col <- ifelse(V8_var[subscripts] < 50,'blue','orange')
         
         pch <- ifelse(V8_var[subscripts] < 50,2,6)
         
           panel.xyplot(x,type='p',col = col,pch = pch)
         
       })

但是，当我在 panel.xyplot 或 ifelse 循环中使用 if 时，这不起作用：

xyplot(V8 ~ V7,'orange')
         ifelse(
           V8_var[subscripts] < 50,panel.xyplot(x,pch = 2),pch = 6)
         )
         
       })

xyplot(V8 ~ V7,'orange')
         
         if(V8_var[subscripts] < 50){
           panel.xyplot(x,pch = 2)
           } else {
           panel.xyplot(x,pch = 6)
           }
       }) 

使用 if 语句也会给出警告：

Warning message:
In if (V8_var[subscripts] < 50) { :
  the condition has length > 1 and only the first element will be used

解决这个问题的方法是通过 if 或 ifelse 语句获取变量值，然后将它们插入任何 panel.xyplot 语句之外的 if，但我这样做不明白当 ifelse 在其中时，为什么 panel.xyplot 语句不能像我预期的那样工作？

会话信息：

R version 4.0.2 (2020-06-22)
Platform: x86_64-apple-darwin17.0 (64-bit)
Running under: macOS Mojave 10.14.6

Matrix products: default
BLAS:   /System/Library/Frameworks/Accelerate.framework/Versions/A/Frameworks/vecLib.framework/Versions/A/libBLAS.dylib
LAPACK: /Library/Frameworks/R.framework/Versions/4.0/Resources/lib/libRlapack.dylib

locale:
[1] en_GB.UTF-8/en_GB.UTF-8/en_GB.UTF-8/C/en_GB.UTF-8/en_GB.UTF-8

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
[1] lattice_0.20-41 cluster_2.1.0  

loaded via a namespace (and not attached):
[1] compiler_4.0.2 tools_4.0.2    grid_4.0.2 

解决方法

panel.xyplot 不能是 ifelse 的参数。以与代码计算col相同的方式计算pch：

library(cluster)
library(lattice)
xyplot(V8 ~ V7,data = flower,V8_var = flower$V8,panel = function(x,y,...,V8_var,subscripts) {
         
         col <- ifelse(V8_var[subscripts] < 50,'blue','orange')
         pch <- ifelse(V8_var[subscripts] < 50,2,6)
         panel.xyplot(x,type='p',col = col,pch = pch)
         
       })

尽管在这种情况下您甚至不需要面板功能：

xyplot(V8 ~ V7,col = ifelse(flower$V8 < 50,"blue","orange"),pch = ifelse(flower$V8 < 50,6))