Finding row index of value change/signal switch

Question

I have a data table of binary signal bursts over time. Those signals bursts are of random length. So I need to find the row index where a change from 0 to 1 (the start point), and the row index where a change of 1 to 0 (the end point) takes place. So that eventually I can find the start and end time of each signal burst.

How would I do that?

Probably with `rle`. But to get better advice, provide some example data and see the suggestions [here](http://stackoverflow.com/q/5963269/210673). — Aaron left Stack Overflow, Jul 16 '13 at 23:14

asb · Answer 1 · 2013-07-16T23:54:00.380

Assuming your data looks like this:

R> x
      V1 V2 V3 V4 V5
 [1,]  0  0  0  0  1
 [2,]  0  1  0  0  1
 [3,]  1  1  0  0  1
 [4,]  1  1  0  0  1
 [5,]  1  1  1  0  1
 [6,]  1  1  1  0  1
 [7,]  1  1  1  0  0
 [8,]  1  1  1  0  0
 [9,]  1  1  1  0  0
[10,]  1  1  1  1  0
[11,]  1  0  1  1  0
[12,]  1  0  1  1  0
[13,]  1  0  1  1  0
[14,]  1  0  1  1  0
[15,]  1  0  1  1  0
[16,]  1  0  1  1  0
[17,]  1  0  1  1  0
[18,]  0  0  1  1  0
[19,]  0  0  1  0  0
[20,]  0  0  1  0  0

I will do this:

apply(x, 2,
      function (k) {
        w <- which(k == 1, arr.ind=TRUE)
        c(head(w, 1), tail(w, 1))
      })

    V1 V2 V3 V4 V5
[1,]  3  2  5 10  1
[2,] 17 10 20 18  6

score 1 · Answer 2 · answered Jul 16 '13 at 23:33

You can use diff or rle as mentioned in the comment. But you should provide :

a signal example
```
 set.seed(1)
 rr <- rbinom(30,1,0.5)
```
What have you tried? Using diff for example I do the following
```
ind <- c(0,diff(rr))
```

The expected output?

start <- min(which(ind==1)) ##  change from 0 to 1 (the start point)
end <- max(which(ind==-1))  ##  change of 1 to 0 (the end point)

Finding row index of value change/signal switch

2 Answers2