R help - Jan 2009 - Splitting a data frame with break points where factor changes value

I have a data frame called s3.  This data frame has a column called
saccade which has two levels 1 and -1.

 > head(s3$saccade, 100)
 [1] NA NA NA NA -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1
 [26] -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1  1  1  1
 [51]  1  1  1  1  1  1  1  1  1  1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1
 [76] -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1

How can I split this data frame into blocks such that a new block
begins when the value in s3$saccade changes?  Split doesn't seem to work
here.  It's important the solution is efficient because the data frame
is huge.

Thanks!

 Titus

Here is one approach.  You might want to change NAs to 0 if you want
them included in the split

set.seed(1)
x <- sample(c(1, -1), 30, TRUE)
x
# determine where changes occur
change <- cumsum(c(0, diff(x) != 0))
change
split(x, change)


On Sat, Jan 31, 2009 at 5:25 AM, Titus von der Malsburg
<malsburg at gmail.com> wrote:
> I have a data frame called s3.  This data frame has a column called
> saccade which has two levels 1 and -1.
>
>  > head(s3$saccade, 100)
>  [1] NA NA NA NA -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1
-1 -1
>  [26] -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1  1 
1  1
>  [51]  1  1  1  1  1  1  1  1  1  1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1
-1 -1
>  [76] -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1
-1 -1
>
> How can I split this data frame into blocks such that a new block
> begins when the value in s3$saccade changes?  Split doesn't seem to
work
> here.  It's important the solution is efficient because the data frame
> is huge.
>
> Thanks!
>
>  Titus
>
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-- 
Jim Holtman
Cincinnati, OH
+1 513 646 9390

What is the problem that you are trying to solve?