I have data that represents different sessions of users. This is in a format like

```
User       StartTime        EndTime
user1      1291043867      1291044055
user2      1290970409      1290972041
user3      1291019561      1291019562
user2      1290897232      1290897244
user1      1291100532      1291100559
user3      1291142492      1291142496
user2      1291128374      1291128391
user2      1291032746      1291032748
...

```

Note that the timestamps are unix times.

I need to get the summary statistics like mean, percentiles on the number of sessions for each user. I also need to get the average time between each successive sessions for all the users. How do I go about doing this in R.