if my data frame looks like this, I want to remove the rows if there is "A" in the A column
df
A B C
1 "4:10:05A" James Math
2 "3:10:45" Tony Science
3 "3:10:55" Hong Math
4 "1:34:23A" Kim Math
5 "2:34:13A: Min English
the result would look like this
df
A B C
2 "3:10:45" Tony Science
3 "3:10:55" Hong Math