Calculate daily means from 5-minute interval data

I forgot in my previous answer, sorry for the duplicated mails.
The function in my previous mail has a na.rm argument, defaulting to FALSE, 
pass na.rm = TRUE to remove the NA's.

agg <- aggregate(cfs ~ date, df1, fun, na.rm = TRUE)

Or simply change the default. I prefer to set na.rm = FALSE because that's 
what R's functions do. And I will only be used to one default, with base R 
functions or my own code.

Hope this helps,