代码如下：
colnames(tab)
>[1] "Year"  "Class" "1"     "2"     "3"     "4"     "5"     "6"     "7"     "8"     "9"     "10"    "11"    "12"   
>tab<-tab[,c("Year","Class",as.character(0:9),">=10")]
>c("Year","Class",as.character(0:9),">=10")
>[1] "Year"  "Class" "0"     "1"     "2"     "3"     "4"     "5"     "6"     "7"     "8"     "9"     ">=10"
出现错误，Error in `[.data.frame`(tab, , c("Year", "Class", as.character(0:9), ">=10")) :
undefined columns selected