Question

Discriminant analysis involves extracting a regression-style linear equation. The equation produced by discriminant analysis is something like as follows:

D = v1*X1 + V2*X3 + V3*X3 + a

How can I extract this equation from the discriminant analysis output in R? I am using the LDA function in the MASS package.

Answer 1

From the ?lda

library(MASS)
Iris <- data.frame(rbind(iris3[,,1], iris3[,,2], iris3[,,3]),
                   Sp = rep(c("s","c","v"), rep(50,3)))
train <- sample(1:150, 75)
table(Iris$Sp[train])
## your answer may differ
##  c  s  v
## 22 23 30
z <- lda(Sp ~ ., Iris, prior = c(1,1,1)/3, subset = train)
predict(z, Iris[-train, ])$class

then you can examine

formula(z)

and look at ?formula