Question

我有一个用于多类分类问题的代码：

data$Class = as.factor(data$Class)
levels(data$Class) <- make.names(levels(factor(data$Class)))
trainIndex <- createDataPartition(data$Class, p = 0.6, list = FALSE, times=1)
trainingSet <- data[ trainIndex,]
testingSet  <- data[-trainIndex,]
train_x <- trainingSet[, -ncol(trainingSet)]
train_y <- trainingSet$Class

testing_x <- testingSet[, -ncol(testingSet)]
testing_y <- testingSet$Class

oneRM <- OneR(trainingSet, verbose = TRUE)
oneRM
summary(oneRM)
plot(oneRM)    

oneRM_pred <- predict(oneRM, testing_x)
oneRM_pred

eval_model(oneRM_pred, testing_y)


AUC_oneRM_pred <- auc(roc(oneRM_pred,testing_y))
cat ("AUC=", oneRM_pred)

# Recall-Precision curve    
oneRM_prediction <- prediction(oneRM_pred, testing_y)
RP.perf <- performance(oneRM_prediction, "tpr", "fpr")

plot (RP.perf)

plot(roc(oneRM_pred,testing_y))

但是在此行之后，代码不起作用：

oneRM_prediction <-预测（oneRM_pred，testing_y）

我收到此错误：

预测错误（oneRM_pred，test_y）：预测格式为无效。

此外，我不知道如何轻松获得F1度量。

最后一个问题，在多类分类问题中计算AUC是否有意义？

Answer 1

让我们从F1开始。

假设您正在使用虹膜数据集，首先，我们需要像加载一样加载所有内容，训练模型并执行预测。

library(datasets)
library(caret)
library(OneR)
library(pROC)

trainIndex <- createDataPartition(iris$Species, p = 0.6, list = FALSE, times=1)
trainingSet <- iris[ trainIndex,]
testingSet  <- iris[-trainIndex,]
train_x <- trainingSet[, -ncol(trainingSet)]
train_y <- trainingSet$Species

testing_x <- testingSet[, -ncol(testingSet)]
testing_y <- testingSet$Species

oneRM <- OneR(trainingSet, verbose = TRUE)
oneRM_pred <- predict(oneRM, testing_x)

然后，您应该计算每个类别的精度，召回率和F1。

cm <- as.matrix(confusionMatrix(oneRM_pred, testing_y))
n = sum(cm) # number of instances
nc = nrow(cm) # number of classes
rowsums = apply(cm, 1, sum) # number of instances per class
colsums = apply(cm, 2, sum) # number of predictions per class
diag = diag(cm)  # number of correctly classified instances per class 

precision = diag / colsums 
recall = diag / rowsums 
f1 = 2 * precision * recall / (precision + recall) 

print(" ************ Confusion Matrix ************")
print(cm)
print(" ************ Diag ************")
print(diag)
print(" ************ Precision/Recall/F1 ************")
print(data.frame(precision, recall, f1))

之后，您可以找到宏F1。

macroPrecision = mean(precision)
macroRecall = mean(recall)
macroF1 = mean(f1)

print(" ************ Macro Precision/Recall/F1 ************")
print(data.frame(macroPrecision, macroRecall, macroF1))

要找到ROC（精确地是AUC），最好使用pROC库。

print(" ************ AUC ************")
roc.multi <- multiclass.roc(testing_y, as.numeric(oneRM_pred))
print(auc(roc.multi))

希望对您有帮助。

在F1和AUC的link上找到详细信息。

Answer 2

如果我以这种方式使用 levels（oneRM_pred）<-levels（testing_y）：

...
oneRM <- OneR(trainingSet, verbose = TRUE)
oneRM
summary(oneRM)
plot(oneRM)    

oneRM_pred <- predict(oneRM, testing_x)
levels(oneRM_pred) <- levels(testing_y)
...

精度比以前大大降低。因此，我不确定是否要强制执行相同的级别是一个好的解决方案。

如何在R中的多类分类问题中计算F1测度和ROC？

2 个答案: