[R] number of patients in a hospital on a given date

RINNER Heinrich H.RINNER at tirol.gv.at
Wed May 14 15:01:58 CEST 2003

Dear R-users!

I am using R 1.7.0, under Windows XP.

Having some hospital discharge data (admission date and discharge date for
each patient), I want to get the number of patients in the hospital on a
given date.

My data look like (simple example):
> x <- data.frame(patid=c("pat1", "pat2"), adm.date = c("15.03.2002",
       dis.date=c("18.03.2002", "17.03.2002"))

I can easily do a date-time conversion from the character objects: 
> x[,2:3] <- apply(x[,2:3], MARGIN=2, FUN=strptime, format="%d.%m.%Y")
> x
  patid   adm.date   dis.date
1  pat1 2002-03-15 2002-03-18
2  pat2 2002-03-16 2002-03-17

What I want in the end is something like a data.frame A like this:
date		no.of.patients
2002-03-14	0
2002-03-15	1
2002-03-16	2
2002-03-17	2
2002-03-18	1
2002-03-19	0

Or, alternatively, a data.frame B like this:
patid	date.in.hospital
pat1	2002-03-15
pat1	2002-03-16
pat1	2002-03-17
pat1	2002-03-18
pat2	2002-03-16
pat2	2002-03-17

>From this I could easily get A by using "table".
So the trick would be to get a data.frame with one line for each day of each
patient in the hospital - but how?

I'd be happy about any ideas,
Heinrich Rinner.

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