如何对R数据帧中的列进行子集化？
可以通过在is.factor中使用sapply创建所有列的对象来将来提取因子列，然后将该对象传递给子集运算符单方括号，从而完成因子列的子集。例如，如果我们有一个包含三列x，y，z的数据帧df，并且其中两个说x和y是因子列，则可以使用Factors<-sapply(df,is.factor)然后使用df[[Factors]，这将仅将数据帧df中的因子列作为子集。
示例
请看以下数据帧-
x1<-as.factor(sample(LETTERS[1:3],20,replace=TRUE))
x2<-as.factor(sample(c("GRP1","GRP2","GRP3","GRP4","GRP5"),20,replace=TRUE))
x3<-sample(1:10,20,replace=TRUE)
df1<-data.frame(x1,x2,x3)
df1输出结果
x1 x2 x3 1 A GRP1 2 2 B GRP1 7 3 B GRP3 1 4 A GRP4 8 5 B GRP2 8 6 A GRP3 6 7 C GRP1 8 8 B GRP3 9 9 B GRP5 1 10 C GRP3 8 11 A GRP3 1 12 C GRP1 1 13 B GRP1 10 14 C GRP1 7 15 C GRP3 10 16 C GRP2 4 17 C GRP2 1 18 B GRP1 2 19 C GRP3 10 20 A GRP2 3
使用sapply创建列对象以使用单个方括号提取因子列-
示例
Factors<-sapply(df1,is.factor) Factors
输出结果
x1 x2 x3 TRUE TRUE FALSE
提取因子列-
示例
Factors_df1<-df1[,Factors] Factors_df1
输出结果
x1 x2 1 A GRP1 2 B GRP1 3 B GRP3 4 A GRP4 5 B GRP2 6 A GRP3 7 C GRP1 8 B GRP3 9 B GRP5 10 C GRP3 11 A GRP3 12 C GRP1 13 B GRP1 14 C GRP1 15 C GRP3 16 C GRP2 17 C GRP2 18 B GRP1 19 C GRP3 20 A GRP2
让我们看另一个例子-
示例
Salary_Grp<-as.factor(sample(c("20-30","31-40","41-50"),20,replace=TRUE))
Gender<-as.factor(sample(c("Male","Female"),20,replace=TRUE))
Rating<-sample(0:10,20,replace=TRUE)
df2<-data.frame(Salary_Grp,Gender,Rating)
df2输出结果
Salary_Grp Gender Rating 1 20-30 Male 7 2 20-30 Female 8 3 31-40 Male 5 4 41-50 Male 7 5 41-50 Male 6 6 20-30 Male 7 7 20-30 Female 0 8 20-30 Male 5 9 31-40 Female 2 10 20-30 Male 7 11 31-40 Male 8 12 31-40 Female 4 13 20-30 Male 9 14 20-30 Female 5 15 31-40 Male 0 16 20-30 Female 9 17 41-50 Female 10 18 31-40 Female 1 19 31-40 Male 5 20 20-30 Female 3
示例
Factors_df2<-sapply(df2,is.factor) Factors_df2
输出结果
Salary_Grp Gender Rating TRUE TRUE FALSE
示例
Factors_df2<-df2[,Factors_df2] Factors_df2
输出结果
Salary_Grp Gender 1 20-30 Male 2 20-30 Female 3 31-40 Male 4 41-50 Male 5 41-50 Male 6 20-30 Male 7 20-30 Female 8 20-30 Male 9 31-40 Female 10 20-30 Male 11 31-40 Male 12 31-40 Female 13 20-30 Male 14 20-30 Female 15 31-40 Male 16 20-30 Female 17 41-50 Female 18 31-40 Female 19 31-40 Male 20 20-30 Female