lda只返回LD1

Question

我尝试了以下与lda相关的代码，并且无法理解为什么除了LD1之外它没有返回LD2。

library(MASS)
library(ggplot2)

从here加载函数ggplotLDAPrep()：

ggplotLDAPrep <- function(x){
  if (!is.null(Terms <- x$terms)) {
    data <- model.frame(x)
    X <- model.matrix(delete.response(Terms), data)
    g <- model.response(data)
    xint <- match("(Intercept)", colnames(X), nomatch = 0L)
    if (xint > 0L) 
      X <- X[, -xint, drop = FALSE]
  }
  means <- colMeans(x$means)
  X <- scale(X, center = means, scale = FALSE) %*% x$scaling
  rtrn <- as.data.frame(cbind(X,labels=as.character(g)))
  rtrn <- data.frame(X,labels=as.character(g))
  return(rtrn)
}


test<-iris[grep("setosa|virginica", iris$Species),1:5]
ldaobject <- lda(Species ~ ., data=test)
fitGraph <- ggplotLDAPrep(ldaobject)
ggplot(fitGraph, aes(LD1,LD2, color=labels))+geom_point()
ldaobject

有什么见解？

Answer 1

如@ user20650所述，您需要至少3组才能返回LD1和LD2。 见这个例子：

library(MASS)
library(ggplot2)

ggplotLDAPrep <- function(x){
  if (!is.null(Terms <- x$terms)) {
    data <- model.frame(x)
    X <- model.matrix(delete.response(Terms), data)
    g <- model.response(data)
    xint <- match("(Intercept)", colnames(X), nomatch = 0L)
    if (xint > 0L) 
      X <- X[, -xint, drop = FALSE]
  }
  means <- colMeans(x$means)
  X <- scale(X, center = means, scale = FALSE) %*% x$scaling
  rtrn <- as.data.frame(cbind(X,labels=as.character(g)))
  rtrn <- data.frame(X,labels=as.character(g))
  return(rtrn)
}


test<-iris[grep("setosa|virginica|versicolor", iris$Species),1:5]
ldaobject <- lda(Species ~ ., data=test)
fitGraph <- ggplotLDAPrep(ldaobject)
ggplot(fitGraph, aes(LD1,LD2, color=labels))+geom_point()

ldaobject

> ldaobject
Call:
lda(Species ~ ., data = test)

Prior probabilities of groups:
    setosa versicolor  virginica 
 0.3333333  0.3333333  0.3333333 

Group means:
           Sepal.Length Sepal.Width Petal.Length Petal.Width
setosa            5.006       3.428        1.462       0.246
versicolor        5.936       2.770        4.260       1.326
virginica         6.588       2.974        5.552       2.026

Coefficients of linear discriminants:
                    LD1         LD2
Sepal.Length  0.8293776  0.02410215
Sepal.Width   1.5344731  2.16452123
Petal.Length -2.2012117 -0.93192121
Petal.Width  -2.8104603  2.83918785

Proportion of trace:
   LD1    LD2 
0.9912 0.0088

绘制结果

ggplot(fitGraph, aes(LD1,LD2, color=labels))+

编辑：添加椭圆

此代码主要来自here

    geom_point() + 
    stat_ellipse(aes(x=LD1, y=LD2, fill = labels), alpha = 0.2, geom = "polygon")