[R] Computing row differences in new columns

[Alexander Engelhardt]

(mods: can you un-flag me if I am still flagged?)

Hi,

First, I would convert the DATE column to an integer. I found this by 
quick googling, perhaps as.Date is your weapon of choice:
https://stat.ethz.ch/pipermail/r-help/2008-August/169870.html

For the column generation I think you will have to use a for-loop here:

yourdata$ResultDiff <- 0
yourdata$DateDiff <- 0

for( i in 1:nrow(yourdata) ){
	yourdata$ResultDiff[i] <- yourdata$RESULT[i] - yourdata$RESULT[i+1] # 
should automatically NA the last cell
	yourdata$DateDiff[i] <- yourdata$datenumber[i] - yourdata$datenumber[i+1]
}

where datenumber is your integer column of the date.

-- Alex


Am 21.03.2011 20:38, schrieb Roberto Lodeiro Muller:
>
> -----Original Message-----
> From: Roberto Lodeiro Muller<roberto.muller at doctor.com>
> To: roberto.muller at doctor.com
> Sent: Mon, Mar 21, 2011 3:37 pm
> Subject: Re: [R] Computing row differences in new columns
>
>
> Sorry, my data appeared badly formatted to me, so I converted it to plain text:
>
> And just to clarify, for each subject in the first row it should appear the difference to the next row, so that the last entry on each subject would be a NA.
>
> Thanks again for your help
>
> Roberto
>
> SUBJECT    DATE       RESULT     DateDiff   ResultDiff
> 10751      22-Jul-03  3.5
> 10751      13-Feb-04  1.3
> 10751      20-Aug-04  1.6
> 10751      08-Mar-05  1.7
> 10751      30-Aug-05  1.6
> 10751      21-Feb-06  1.3
> 10751      31-Aug-06  1.2
> 10751      27-Feb-07  1.5
> 10751      29-Aug-07  1
> 10752      29-Jul-03  5.9
> 10752      24-Feb-04  5
> 10752      25-Aug-04  3.6
> 10752      11-Mar-05  5.1
> 10752      18-Sep-05  2.2
> 10752      23-Feb-06  3.1
> 10752      24-Aug-06  3.7
> 10752      27-Feb-07  6