[R] ifelse to speed up loop?

[arun]

Hi,

I guess you meant:
c(TRUE, cumsum( v[-length(v)] != v[-1] ))
 [1] 1 0 0 1 1 1 2 2 2 3 3 3
this:
 cumsum(c(TRUE, v[-length(v)] != v[-1] ))
# [1] 1 1 1 2 2 2 3 3 3 4 4 4
A.K.




----- Original Message -----
From: William Dunlap <wdunlap at tibco.com>
To: arun <smartpink111 at yahoo.com>; Jeffrey Fuerte <fuertejn at vcu.edu>
Cc: R help <r-help at r-project.org>
Sent: Thursday, January 24, 2013 6:48 PM
Subject: RE: [R] ifelse to speed up loop?

I like
   v <- test[,1]
   c(TRUE, cumsum( v[-length(v)] != v[-1] ))
(R's arithmetic on logicals treats TRUE as 1 and FALSE as 0.)

Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com


> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On Behalf
> Of arun
> Sent: Thursday, January 24, 2013 3:37 PM
> To: Jeffrey Fuerte
> Cc: R help
> Subject: Re: [R] ifelse to speed up loop?
> 
> HI,
> 
> This might be better.
> test$group<-cumsum(abs(c(1,diff(test[,1]))))
> A.K.
> 
> 
> 
> 
> ----- Original Message -----
> From: Jeffrey Fuerte <fuertejn at vcu.edu>
> To: r-help at r-project.org
> Cc:
> Sent: Thursday, January 24, 2013 4:20 PM
> Subject: [R] ifelse to speed up loop?
> 
> Hello,
> 
> I'm not sure how to explain what I'm looking for but essentially I have a
> test dataset that looks like this:
> 
> test:
>    V1
> 1   1
> 2   1
> 3   1
> 4   2
> 5   2
> 6   2
> 7   1
> 8   1
> 9   1
> 10  2
> 11  2
> 12  2
> 
> And what I want to be able to do is create another column that captures a
> "grouping" variable that looks like this:
> 
> test
>    V1 group
> 1   1  1
> 2   1  1
> 3   1  1
> 4   2  2
> 5   2  2
> 6   2  2
> 7   1 3
> 8   1  3
> 9   1  3
> 10  2  4
> 11  2  4
> 12  2  4
> 
> So, it's keeping track of the changes in V1, but even though V1 could be
> the same in different instances, the group is treating it as a new group.
> I have written a loop that does what I want, but this takes too long to
> run, so I was hoping for either a faster approach or an ifelse statement.
> Any ideas?
> 
> By the loop I was using looks like this:
> 
> groupings <- 1
> test$group[1] <- groupings
> for (i in 2:length(test$V1))
> {
> if (test$V1[i]==test$V1[i-1])
> {
> test$group[i] <- groupings
> } else {
> groupings <- groupings+1
> test$group[i] <- groupings
> }
> }
> 
> Thanks for the help.
> 
>     [[alternative HTML version deleted]]
> 
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> R-help at r-project.org mailing list
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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.