(For the record, I agree with @dsaxton. But just to give you something, here is a quick demonstration of using LDA to optimally bin a continuous variable based on a factor.)
library(MASS)
Iris = iris[,c(1,5)]
model = lda(Species~Sepal.Length, Iris)
range(Iris$Sepal.Length) # [1] 4.3 7.9
cbind(seq(4, 8, .1),
predict(model, data.frame(Sepal.Length=seq(4, 8, .1)))$$Sepal.Length) # [1] 4.3 7.9
cbind(seq(4, 8, .1),
predict(model, data.frame(Sepal.Length=seq(4, 8, .1)))$class)
# [,1] [,2]
# [1,] 4.0 1
# [2,] 4.1 1
# ...
# [15,] 5.4 1
# [16,] 5.5 2
# [17,] 5.6 2
# ...
# [23,] 6.2 2
# [24,] 6.3 3
# [25,] 6.4 3
# ...
# [41,] 8.0 3