从数据帧中删除因子级别

Question

我从kaggle下载了泰坦尼克号火车数据集：

我的代码是：

df = read.csv('titanic.csv', header=TRUE)
df$Pclass = as.factor(df$Pclass)
df$Survived = as.factor(df$Survived)
df = df[,c(2,3,5,6,12)]
df = na.omit(df)
rownames(df) <- 1:nrow(df)
df$Age[df$Age <= 18] = "child"
df$Age[(df$Age > 18) & (df$Age <= 60) & (df$Age != "child")] = "adult"
df$Age[(df$Age != "child") & (df$Age != "adult")] = "senior"
df$Age = as.factor(df$Age)
summary(df)

此时总结的结果是：

 Survived Pclass      Sex          Age      Embarked
 0:424    1:186   female:261   adult :553    :  2   
 1:290    2:173   male  :453   child :139   C:130   
          3:355                senior: 22   Q: 28   
                                            S:554 

我的问题是上载变量：

barplot(table(df$Embarked), xlab="Port of Embarkment", ylab="Frequency", main="Histograma de la variable \n Embarked")

barplot output

登船高度

> levels(df$Embarked)
[1] ""  "C" "Q" "S"

这是我的问题，这是第一个级别：“”（空），我找不到删除它的方法。我一直在测试无法在Stackoverflow中找到的几种方法，但无法解决我的问题。

Answer 1

删除带有空值的行后，重构：

df <- df[df$Embarked!="",]
df$Embarked <- factor(df$Embarked)
barplot(table(df$Embarked), xlab="Port of Embarkment", 
        ylab="Frequency", main="Histograma de la variable \n Embarked")