Splitting a time + duration into a series of periods
Travers -
R's date/time abilities are pretty powerful -- you shouldn't have to
resort to outside programs. Here's how I'd approach the problem:
dat = read.csv(textConnection('user, login_time, session_min
+ alice, 2010/01/01 10:00, 145 + bob, 2010/01/01 11:00, 30 + '),stringsAsFactors=FALSE)
dat$login_time = as.POSIXct(dat$login_time)
dat$login_end = dat$login_time + 60 * dat$session_min
tms = seq(as.POSIXct('2010/01/01 10:00'),
+ as.POSIXct('2010/01/01 12:30'),by=30*60)
data.frame(time=tms,count=sapply(tms,
+ function(tm)sum(dat$login_time <= tm & dat$login_end > tm)))
time count
1 2010-01-01 10:00:00 1
2 2010-01-01 10:30:00 1
3 2010-01-01 11:00:00 2
4 2010-01-01 11:30:00 1
5 2010-01-01 12:00:00 1
6 2010-01-01 12:30:00 0
Hope this helps.
- Phil Spector
Statistical Computing Facility
Department of Statistics
UC Berkeley
spector at stat.berkeley.edu
On Fri, 24 Sep 2010, Travers Naran wrote:
Hi all, Here's what I have. I have a list of log-in times for users and how long their sessions were. user, login_time, session_min alice, 2010/01/01 10:00, 145 bob, 2010/01/01 11:00, 30 What I want to do is create a bar chart showing, in 1/2 hour segments, the number of users logged in at the same time. For example: 10:00 1 10:30 1 11:00 2 11:30 1 The only way I can do this now is to send the data through a Perl script to generate raw data like: alice, 2010/01/01, 10:00 alice, 2010/01/01, 10:30 alice, 2010/01/01, 11:00 ... bob, 2010/01/01, 11:00 I've looked through the man pages for a couple hours now, and I can't find a better of way of doing this directly in R. Any help or pointers? Thanks in advance.
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