# Re: [R] sequentially process a list

From: jim holtman <jholtman_at_gmail.com>
Date: Mon, 21 May 2007 12:15:09 -0400

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
+ "
```

> # 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_at_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_at_stat.math.ethz.ch mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> 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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