R help - May 2007 - sequentially process a list

Hi dear R users,

I'm a R beginner and I have a basic question about sequential treatments of
lists.

I have a time based (i.e. events are consecutive) list of values of a biological
property.

Like :

time  value
1        5
2        10  
3      7
4      10
5      19
6      21
7      20
8      18
9      10
10      7
11      8
12      12
13      17
14      19
15      24
16      18
17      15
18      10
19      9
[...]


And I have to define a threshold and to attach each event to his group, i.e.
values upper the threshold.

Like, for a threshold value of 17

time  value   group
1        5       NA
2        10      NA
3      7      NA
4      10      NA
5      19      1
6      21      1
7      20      1
8      18      1
9      10      NA
10      7      NA
11      8      NA
12      12      NA
13      17      2
14      19      2
15      24      2
16      18      2
17      15      NA
18      10      NA
19      9      NA
[...]


The only solution that I have found is to do a sequentially read and write :
for(i in 1:length(my_events_list))
{
    [...]
}

But I very slow. Do you have another ideas ?

And after I need to extract maximum values for each group
Like :
group        max_value
1            21
2            24
[...]

and for each event which is part of a group to know if is't a ascending
phase or no.


Yes, lot of questions !! Sorry, but I think that the solution may be unique.

In advance, thank you a lot

regards

JS







     
_____________________________________________________________________________

Try nested ifelse() statements to label the group

ex.
time$group=ifelse(time$time<5,NA,
	ifelse(time$time<9,1,
		ifelse(time$time<13,NA,
			ifelse(time$time<17,2,NA)
		)
	)
)

Then use aggregate to find the max value.

ex.
time.max=aggregate(time$value,list(group=time$group),max)


On 21-May-07, at 6:39 AM, Robert wrote:
> Hi dear R users,
>
> I'm a R beginner and I have a basic question about sequential  
> treatments of lists.
>
> I have a time based (i.e. events are consecutive) list of values of  
> a biological property.
>
> Like :
>
> time  value
> 1        5
> 2        10
> 3      7
> 4      10
> 5      19
> 6      21
> 7      20
> 8      18
> 9      10
> 10      7
> 11      8
> 12      12
> 13      17
> 14      19
> 15      24
> 16      18
> 17      15
> 18      10
> 19      9
> [...]
>
>
> And I have to define a threshold and to attach each event to his  
> group, i.e. values upper the threshold.
>
> Like, for a threshold value of 17
>
> time  value   group
> 1        5       NA
> 2        10      NA
> 3      7      NA
> 4      10      NA
> 5      19      1
> 6      21      1
> 7      20      1
> 8      18      1
> 9      10      NA
> 10      7      NA
> 11      8      NA
> 12      12      NA
> 13      17      2
> 14      19      2
> 15      24      2
> 16      18      2
> 17      15      NA
> 18      10      NA
> 19      9      NA
> [...]
>
>
> The only solution that I have found is to do a sequentially read  
> and write :
> for(i in 1:length(my_events_list))
> {
>     [...]
> }
>
> But I very slow. Do you have another ideas ?
>
> And after I need to extract maximum values for each group
> Like :
> group        max_value
> 1            21
> 2            24
> [...]
>
> and for each event which is part of a group to know if is't a  
> ascending phase or no.
>
>
> Yes, lot of questions !! Sorry, but I think that the solution may  
> be unique.
>
> In advance, thank you a lot
>
> regards
>
> JS
>
>
>
>
>
>
>
>        
> ______________________________________________________________________ 
> _______
>
> ______________________________________________
> R-help at stat.math.ethz.ch 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.
--
Mike Lawrence
Graduate Student, Dalhousie University Department of Psychology
http://myweb.dal.ca/mc973993

"The road to wisdom? Well, it's plain and simple to express:
Err and err and err again, but less and less and less."
- Piet Hein

This should do it for you.  It makes use of 'rle' to find the
'runs' of
thresholds and then changes the values to the sequence numbers
> x <- "time  value
+ 1        5
+ 2        10
+ 3      7
+ 4      10
+ 5      19
+ 6      21
+ 7      20
+ 8      18
+ 9      10
+ 10      7
+ 11      8
+ 12      12
+ 13      17
+ 14      19
+ 15      24
+ 16      18
+ 17      15
+ 18      10
+ 19      9
+ "
> x <- read.table(textConnection(x), header=TRUE)
> # find the 'runs' of thresholds
> threshold <- rle(x$value >= 17)
> # get offset of each group
> offset <- cumsum(c(1,threshold$lengths))
> # create sequence numbers for the groups
> seqNum <- cumsum(threshold$value)
> # compute the indices of where the thresholds are
> x$group <- NA  # initialize the vector
> # change the values for the groups
> for (i in which(threshold$value)){
+     x$group[seq(offset[i], length=threshold$length[i])] <- seqNum[i]
+ }
> # extract max for each group
> x
   time value group
1     1     5    NA
2     2    10    NA
3     3     7    NA
4     4    10    NA
5     5    19     1
6     6    21     1
7     7    20     1
8     8    18     1
9     9    10    NA
10   10     7    NA
11   11     8    NA
12   12    12    NA
13   13    17     2
14   14    19     2
15   15    24     2
16   16    18     2
17   17    15    NA
18   18    10    NA
19   19     9    NA
> tapply(x$value, x$group, max)
 1  2
21 24



On 5/21/07, Robert <jsubei@yahoo.fr> wrote:
>
> Hi dear R users,
>
> I'm a R beginner and I have a basic question about sequential
treatments
> of lists.
>
> I have a time based (i.e. events are consecutive) list of values of a
> biological property.
>
> Like :
>
> time  value
> 1        5
> 2        10
> 3      7
> 4      10
> 5      19
> 6      21
> 7      20
> 8      18
> 9      10
> 10      7
> 11      8
> 12      12
> 13      17
> 14      19
> 15      24
> 16      18
> 17      15
> 18      10
> 19      9
> [...]
>
>
> And I have to define a threshold and to attach each event to his group,
> i.e. values upper the threshold.
>
> Like, for a threshold value of 17
>
> time  value   group
> 1        5       NA
> 2        10      NA
> 3      7      NA
> 4      10      NA
> 5      19      1
> 6      21      1
> 7      20      1
> 8      18      1
> 9      10      NA
> 10      7      NA
> 11      8      NA
> 12      12      NA
> 13      17      2
> 14      19      2
> 15      24      2
> 16      18      2
> 17      15      NA
> 18      10      NA
> 19      9      NA
> [...]
>
>
> The only solution that I have found is to do a sequentially read and write
> :
> for(i in 1:length(my_events_list))
> {
>    [...]
> }
>
> But I very slow. Do you have another ideas ?
>
> And after I need to extract maximum values for each group
> Like :
> group        max_value
> 1            21
> 2            24
> [...]
>
> and for each event which is part of a group to know if is't a ascending
> phase or no.
>
>
> Yes, lot of questions !! Sorry, but I think that the solution may be
> unique.
>
> In advance, thank you a lot
>
> regards
>
> JS
>
>
>
>
>
>
>
>
>
_____________________________________________________________________________
>
> ______________________________________________
> R-help@stat.math.ethz.ch 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.
>


-- 
Jim Holtman
Cincinnati, OH
+1 513 646 9390

What is the problem you are trying to solve?

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