[R] Finding an average time spent

[Jim Lemon]

On 08/13/2011 06:23 AM, erinbspace wrote:
> Hello R help!
>
> I am extremely new to R (as in 3 just days) and I've been using it to do
> some pretty basic things. I am frustratingly stuck on one point, and am so
> so so close to figuring it out, but just far enough away to ask for some
> (perhaps embarrassingly easy) help.
>
> I have a dataset, visitors, that has a variable called Time.Spent.
> Time.Spent consists of times in the format hh:mm:ss , and it is a
> measurement, kind of like a timer, of the amount of time someone spent in a
> museum exhibit.
>
> I need to find the average time spent.  I've figured the easiest way to do
> this would be to convert it into seconds. I found a function that someone
> wrote on how to do this here:
> http://stackoverflow.com/questions/1389428/dealing-with-time-periods-such-as-5-minutes-and-30-seconds-in-r
>
> I thought this would be the answer! However, when I run the code, it works
> perfectly for the first variable in the first observation, but then repeats
> the same answer all the way down the rows.
>
> Sorry for the wordiness, here's the code I have:
>
> # The function to convert hh:mm:ss into just seconds:
>
> time.to.seconds<- function(time) {
>     time<- strsplit(time, ":")[[1]]
>     return ((as.numeric(time[1]) * 60 * 60) + (as.numeric(time[2]) * 60) +
> (as.numeric(time[3])))
> }
>
> # I've tried many things to then create a new variable in the dataset
> visitors:
>
> visitors$TimeInSeconds<- time.to.seconds(time=c(visitors$Time.Spent))
>
> # Or
>
> visitors$TimeInSeconds<- time.to.seconds(visitors$Time.Spent)
>
>
> I figure it has something to do with the fact that strsplit() makes a list?
> Do I need a loop to go through each variable? I know this is a huge question
> but any hints at al would be very much appreciated.
>
Hi erinbspace,
By hard coding the [[1]] in your function, you are automatically taking 
the first element of any list. If you want to convert a vector of times, 
try this:

time.to.seconds<- function(time) {
  time<-strsplit(time, ":")[[1]]
  return(as.numeric(time[1]) * 3600 + as.numeric(time[2]) * 60 +
   as.numeric(time[3]))
}
watch.times<-c("0:2:31","0:4:12","0:0:47")
# use sapply to step through the vector of times
sapply(watch.times,time.to.seconds)
0:2:31 0:4:12 0:0:47
    151    252     47

Jim