sapply

R: Using sapply on vector of POSIXct

I have what may be a very simple question. I want to process a column of POSIXct objects from a dataframe and generate a vector of datetime strings. I tried to use the following sapply call dt <- sapply(df$datetime, function(x) format(x,"%Y-%m-%dT%H:%M:%S")) but to no avail. I keep getting the following error: Error in prettyNu...

vector of POSIXct and sapply

What if you want to apply a function other than format to a list of POSIXct objects? For instance, say I want to take a vector of times, truncate those times to the hour, and apply an arbitrary function to each one of those times. > obs.times=as.POSIXct(c('2010-01-02 12:37:45','2010-01-02 08:45:45','2010-01-09 14:45:53')) > obs.truncat...