R help - Jan 2013 - 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]]

Your query is a little unclear to me, but I suspect
?rle
is what you want.

-- Bert

On Thu, Jan 24, 2013 at 1:20 PM, Jeffrey Fuerte <fuertejn at vcu.edu>
wrote:
> 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]]
>
> ______________________________________________
> R-help at 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.


-- 

Bert Gunter
Genentech Nonclinical Biostatistics

Internal Contact Info:
Phone: 467-7374
Website:
http://pharmadevelopment.roche.com/index/pdb/pdb-functional-groups/pdb-biostatistics/pdb-ncb-home.htm

Hi,
You could do this:
test<-read.table(text="
? 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
",sep="",header=T)

?test$Group<-cumsum(abs(c(0,diff(test[,1]))))+1
test
#?? V1 Group
#1?? 1???? 1
#2?? 1???? 1
#3?? 1???? 1
#4?? 2???? 2
#5?? 2???? 2
#6?? 2???? 2
#7?? 1???? 3
#?? 1???? 3
#9?? 1???? 3
#10? 2???? 4
#11? 2???? 4
#12? 2???? 4
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]]

______________________________________________
R-help at 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.

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]]

______________________________________________
R-help at 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.