how to remove rows with missing factor value in it?

["Danni Wang" <wangdn@uclink4.berkeley.edu>]

Hi, Group,

My input table have a timestamp column (such as 13:14:15), which has missing
values. It is treated as strings.
data[!is.na(data$timestamp),] couldn't work.

Do you know how to remove those rows?

Thanks,
Danni