从存储在“变量”中的数据中删除列

So I loaded few csv files:

所以我加载了几个csv文件：

tbl = list.files(pattern="*.csv")
> tbl
 [1] "F1.csv"  "F10.csv" "F11.csv" "F12.csv" "F13.csv" "F14.csv" "F15.csv" "F16.csv"
 [9] "F17.csv" "F18.csv" "F19.csv" "F2.csv"  "F20.csv" "F3.csv"  "F4.csv"  "F5.csv" 
[17] "F6.csv"  "F7.csv"  "F8.csv"  "F9.csv" 
t