try this:

> x <- scan(textConnection("30/01/2007      0
+ 31/01/2007      -1
+ 01/02/2007      -1
+ 02/02/2007      -1
+ 03/02/2007      1
+ 04/02/2007      1
+ 05/02/2007      1
+ 06/02/2007      1
+ 07/02/2007      1
+ 08/02/2007      1
+ 09/02/2007      0
+ 10/02/2007      0
+ 11/02/2007      0
+ 12/02/2007      1
+ 13/02/2007      1
+ 14/02/2007      1
+ 15/02/2007      0
+ 16/02/2007      0
+ "), what=list(date="", value=0))
Read 18 records
> x$date <- as.Date(x$date, "%d/%m/%Y")
> # determine the breaks
> x.breaks <- c(TRUE, diff(x$value) != 0)
> # determine the value at the break; assume that it is the minimum
> x.bdate <- x$date[x.breaks]
> data.frame(date=x.bdate[cumsum(x.breaks)], value=x$value)
         date value
1  2007-01-30     0
2  2007-01-31    -1
3  2007-01-31    -1
4  2007-01-31    -1
5  2007-02-03     1
6  2007-02-03     1
7  2007-02-03     1
8  2007-02-03     1
9  2007-02-03     1
10 2007-02-03     1
11 2007-02-09     0
12 2007-02-09     0
13 2007-02-09     0
14 2007-02-12     1
15 2007-02-12     1
16 2007-02-12     1
17 2007-02-15     0
18 2007-02-15     0
>
>
>



On 2/16/07, Murali Menon <feanor0@hotmail.com> wrote:
>
> Folks,
>
> I have a dataframe comprising a column of dates and a column of signals
> (-1,
> 0, 1) that looks something like this:
>
> 30/01/2007      0
> 31/01/2007      -1
> 01/02/2007      -1
> 02/02/2007      -1
> 03/02/2007      1
> 04/02/2007      1
> 05/02/2007      1
> 06/02/2007      1
> 07/02/2007      1
> 08/02/2007      1
> 09/02/2007      0
> 10/02/2007      0
> 11/02/2007      0
> 12/02/2007      1
> 13/02/2007      1
> 14/02/2007      1
> 15/02/2007      0
> 16/02/2007      0
>
> What I need to do is for each signal *in reverse chronological order* to
> find the date that it first appeared. So, for the zero on 16/02/2007 and
> 15/02/2007, the 'inception' date would be 15/02/2007, because the day
> before, the signal was 1. Likewise, the 'inception' date for the signal 1
> on
> 08/02/2007 and the five days prior, would be 03/02/2007. I need to create
> a
> structure of inception dates that would finally look as follows:
>
> -1      31/01/2007
> -1      31/01/2007
> -1      31/01/2007
> 1       03/02/2007
> 1       03/02/2007
> 1       03/02/2007
> 1       03/02/2007
> 1       03/02/2007
> 1       03/02/2007
> 0       09/02/2007
> 0       09/02/2007
> 0       09/02/2007
> 1       12/02/2007
> 1       12/02/2007
> 1       12/02/2007
> 0       15/02/2007
> 0       15/02/2007
>
> Is there a clever way of doing this? My sadly C-oriented upbringing can
> only
> think in terms of for-loops.
>
> Thanks!
>
> Murali
>
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> 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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