这是我在 Rstudio 中的脚本：

library(class)
library(ggplot2)
library(gmodels)
library(scales)
library(caret)
library(tidyverse)
library(caret)

db_data <- iris
row_train <- sample(nrow(iris), nrow(iris)*0.8)
db_train <- iris[row_train,]
db_test <- iris[-row_train,]

unique(db_train$Species)
table(db_train$Species)
#--------

#KNN
#-------
model_knn<-train(Species ~ ., data = db_train, method = "knn",tuneGrid = data.frame(k = 12))
summary(model_knn)
#-------

#PREDICTION NEW RECORD
#-------
test_data <- db_test
db_test$predict <- predict(model_knn, newdata=test_data, interval='confidence')
confusionMatrix(data=factor(db_test$predict),reference=factor(db_test$Species))
#-------

如何在 KNN 模型中定义 k 的最佳值？