> -----Original Message-----
> From: r-help-boun...@r-project.org
> [mailto:r-help-boun...@r-project.org] On Behalf Of William Dunlap
> Sent: Friday, December 04, 2009 3:29 PM
> To: Dennis Fisher; r-h...@stat.math.ethz.ch
> Subject: Re: [R] Use of apply rather than a loop
>
> You could try using merge:
>
> >
> d<-data.frame(Subject=rep(11:13,each=3),Time=101:109,Marker=c(0,1,0,
> 0,0,0, 0,0,1))
> > d
> Subject Time Marker
> 1 11 101 0
> 2 11 102 1
> 3 11 103 0
> 4 12 104 0
> 5 12 105 0
> 6 12 106 0
> 7 13 107 0
> 8 13 108 0
> 9 13 109 1
> > d$Time - merge(d,d[d$Marker==1,],by="Subject",all.x=TRUE)$Time.y
> [1] -1 0 1 NA NA NA -2 -1 0
merge() can rearrange the rows of the data.frame so I should
have diff'ed 2 columns from the merged data.frame, not one
from the original and one from the merged. E.g.,
> d <- d[sample(nrow(d)),] # scramble rows
> dm <- merge(d,d[d$Marker==1,],by="Subject",all.x=TRUE,
suffixes=c("", "Marked"))
> dm$TimeMinusMarkedTime <- dm$Time - NAtoZero(dm$TimeMarked)
> dm <- dm[ with(dm, order(Subject, Time)), ] # put into nice order
> dm$TimeMinusMarkedTime
[1] -1 0 1 NA NA NA -2 -1 0
> dm
Subject Time Marker TimeMarked MarkerMarked TimeMinusMarkedTime
3 11 101 0 102 1 -1
1 11 102 1 102 1 0
2 11 103 0 102 1 1
5 12 104 0 NA NA 104
4 12 105 0 NA NA 105
6 12 106 0 NA NA 106
7 13 107 0 109 1 -2
9 13 108 0 109 1 -1
8 13 109 1 109 1 0
When there are lots of unique values in Subject this
is considerably faster than any sort of looping approach.
Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com
>
> If you want the reference times for Subjects without a
> marked instance to be 0, replace the NA's in Time.y by 0:
> > NAtoZero<-function(x){ x[is.na(x)]<-0 ; x }
> > d$Time -
> NAtoZero(merge(d,d[d$Marker==1,],by="Subject",all.x=TRUE)$Time.y)
> [1] -1 0 1 104 105 106 -2 -1 0
>
> If there is more than one marked instance for
> a given subject this method will fail.
>
> Bill Dunlap
> Spotfire, TIBCO Software
> wdunlap tibco.com
>
> > -----Original Message-----
> > From: r-help-boun...@r-project.org
> > [mailto:r-help-boun...@r-project.org] On Behalf Of Dennis Fisher
> > Sent: Friday, December 04, 2009 2:47 PM
> > To: r-h...@stat.math.ethz.ch
> > Subject: [R] Use of apply rather than a loop
> >
> > Colleagues,
> >
> > R 2.9.0 on all platforms
> >
> > I have a dataset that contains three columns of interest:
> > ID's, serial
> > elapsed times, and a marker. Representative data:
> > Subject Time Marker
> > 1 100.5 0
> > 1 101 0
> > 1 102 1
> > 1 103 0
> > 1 105 0
> >
> > For each subject, I would like to find the time associated
> > with MARKER
> > == 1, then replace Time with Time - (Time[Marker == 1])
> > The result for this subject would be:
> > Subject Time Marker
> > 1 -1.5 0
> > 1 -1 0
> > 1 0 1
> > 1 1 0
> > 1 3 0
> >
> > One proviso: some subjects do not have Marker == 1; for these
> > subjects, I would like Time to remain unchanged.
> >
> > At present, I am looping over each subject. The number of
> > subjects is
> > large so this process is quite slow. I assume that one of
> the apply
> > functions could speed this markedly but I am not facile
> with them.
> > Any help would be appreciated.
> >
> > Dennis
> >
> > Dennis Fisher MD
> > P < (The "P Less Than" Company)
> > Phone: 1-866-PLessThan (1-866-753-7784)
> > Fax: 1-866-PLessThan (1-866-753-7784)
> > www.PLessThan.com
> >
> > ______________________________________________
> > R-help@r-project.org mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-help
> > PLEASE do read the posting guide
> > http://www.R-project.org/posting-guide.html
> > and provide commented, minimal, self-contained, reproducible code.
> >
>
> ______________________________________________
> R-help@r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
