Nice! It works. Thank you, Rui
 
There's something that takes me back to the original question, though. The code takes the first value that meets the critical condition (light ==0); however, this value can appear more than once a day because these animals nest in dark caves, and once they are in the logger sensor registers a 0. So, a second condition limiting the time at which the critical condition can be accepted to calculate dusk should be implemented; something like (although R doesn't allow to impose the double condition):
 
if (05:00:00<z$clock> 17:00:00) {zrle <- rle(x$lig == 0)}
 
 
Santi

From: Rui Barradas <ruipbarradas@sapo.pt>
>To: Santiago Guallar <sguallar@yahoo.com> 
>Cc: r-help@r-project.org 
>Sent: Wednesday, July 18, 2012 11:37 AM
>Subject: Re: [R] Imposing more than one condition to if
>
>hELLO,
>
>There was no nedd to change the names of the variables inside the 
>fucntion. What was going on s that in this new file column 'dtime' 
>doesn't exist. Since column 'clock' exists in all files, I've changed 
>the function once again, making it more general.
>
>Note that there is an argument 'colTime' with a default value. In the 
>function's use below I call it with and without that argument.
>
>
>f <- function(x, colTime="clock"){
>    zrle <- rle(x$lig == 0)
>    if(zrle$values[1]){
>        idusk <- sum(zrle$lengths[1:2]) + 1
>        idawn <- zrle$lengths[1] + 1
>        x$dusk <- x[ idusk , colTime ]
>        x$dawn <- x[ idawn , colTime ]
>    }else{
>        idusk <- zrle$lengths[1] + 1
>        x$dusk <- x[ idusk , colTime ]
>        x$dawn <- NA
>    }
>    x
>}
>
>str(d)
>#d$date <- as.Date(d$date, format="%d/%m%/y")
>
>#library(chron)
>#tm <- times(as.character(d$clock))
>#d$clock <- tm
>
># See what will happen. This call uses the default 'colTime'
>bb <- by(d, d$date, f)
>for(i in seq_along(bb))    print(head(bb[[i]], 1))
>
># call and rbind. This call uses explicit arg 'colTime'
>do.call(rbind, by(d, d$date, f, colTime="clock"))
>
># Alternatively, it could be, because 'bb' is already created,
>do.call(rbind, bb)
>
>
>In the code above, I use an optional conversion to date and time 
>classes; as.Date is part of base R, but class times needs package chron. 
>It's a good idea to convert these variables, you can later use, say, 
>arithmetics on dates and times, such as differences.
>
>Hope this helps,
>
>Rui Barradas
>
>Em 17-07-2012 19:53, Santiago Guallar escreveu:
>> Thank for your time, Rui.
>> Now, I get this error message:
>> Error en rbind(deparse.level, ...) :
>> numbers of columns of arguments do not match
>> Apparently, some columns have missing values and rbind doesn't work. I
>> tried:
>> require(plyr)
>> do.call(rbind.fill, by(z, z$date, f))
>> Then the code runs through but dusk the variable dusk is missing and
>> dawn is filled with NA.
>> Just in case the problem simply lies in a name, this is your code after
>> I changed the object names (basically 'x' and 'd' by 'z') to adapt them
>> to the names of my dataset:
>> f <- function(z){
>> zrle <- rle(z$lig == 0)
>> if(zrle$values[1]){
>> idusk <- sum(zrle$lengths[1:2]) + 1
>> idawn <- zrle$lengths[1] + 1
>> z$dusk <- z$dtime[ idusk ]
>> z$dawn <- z$dtime[ idawn ]
>> }else{
>> idusk <- zrle$lengths[1] + 1
>> z$dusk <- z$dtime[ idusk ]
>> z$dawn <- NA
>> }
>> z
>> }
>>
>> do.call(rbind, by(z, z$date, f))
>> Again, I attached a dput() with the object z which contains my dataset.
>> Santi
>>
>>    *From:* Rui Barradas <ruipbarradas@sapo.pt>
>>    *To:* Santiago Guallar <sguallar@yahoo.com>
>>    *Cc:* r-help@r-project.org
>>    *Sent:* Tuesday, July 17, 2012 11:52 AM
>>    *Subject:* Re: [R] Imposing more than one condition to if
>>
>>
>>        Hello,
>>
>>        My code couldn't find the right input columns because your real
>>        data has
>>        different names, it could only find the example dataset's names.
>>
>>        And there's another problem, my code would give correct answers
>>        with a
>>        limted number of possible inputs and fail with real data.
>>
>>        Corrected:
>>
>>
>>        f <- function(x){
>>              zrle <- rle(x$lig == 0)
>>              if(zrle$values[1]){
>>                  idusk <- sum(zrle$lengths[1:2]) + 1
>>                  idawn <- zrle$lengths[1] + 1
>>                  x$dusk <- x$dtime[ idusk ]
>>                  x$dawn <- x$dtime[ idawn ]
>>              }else{
>>                  idusk <- zrle$lengths[1] + 1
>>                  x$dusk <- x$dtime[ idusk ]
>>                  x$dawn <- NA
>>              }
>>              x
>>        }
>>
>>        do.call(rbind, by(d, d$date, f))
>>
>>
>>        One more thing, you are reading your dataset into a data.frame
>>        forgetting that character strings become factors. Try str(d) to
>>        see it.
>>        ('d' is the data.frame.) You could/should coerce the date/time
>>        values to
>>        appropriate classes, something like
>>
>>
>>        d$time <- as.character(d$time)
>>        d$time <- as.POSIXct(d$time, format="%d/%m/%y %H:%M:%S")
>>        d$date <- as.character(d$date)
>>        d$date <- as.Date(d$date, format="%d/%m/%y")
>>
>>
>>        Hope this helps,
>>
>>        Rui Barradas
>>
>>        Em 17-07-2012 07:14, Santiago Guallar escreveu:
>>          > Thank you Rui,
>>          >
>>          > When applied to my original data, your code goes through
>>        although it
>>          > does not produce the correct results: for dusk gives the
>>        first time
>>          > value of next day, for dawn it gives NA. It seems that the
>>        function f
>>          > doesn't find the right input columns.
>>          > A, Ilso had to push up the memory size.
>>          > Attached a file (containing just 3000 of the original c.
>>        45000 rows)
>>          > after dput().
>>          >
>>          > Santi
>>          >
>>          >
>>          >
>>        ------------------------------------------------------------------------
>>          >    *From:* Rui Barradas <ruipbarradas@sapo.pt
>>        <mailto:ruipbarradas@sapo.pt>>
>>          >    *To:* Santiago Guallar <sguallar@yahoo.com
>>        <mailto:sguallar@yahoo.com>>
>>          >    *Cc:* r-help@r-project.org <mailto:r-help@r-project.org>
>>          >    *Sent:* Sunday, July 15, 2012 7:21 PM
>>          >    *Subject:* Re: [R] Imposing more than one condition to if
>>          >
>>          > Hello,
>>          >
>>          >    There are obvious bugs in your code, you are testing for
>>        light > 2 or
>>          >    ligth < 2 but this would mean that dusk and dawn are
>>        undetermined for
>>          >    light == 2 and that they happen at light == 1.
>>          >
>>          >    Without loops or compound logical conditions:
>>          >
>>          >
>>          >    f <- function(x){
>>          >          x$dawn <- x$time[ which.min(x$light) ]
>>          >          x$dusk <- x$time[ max(which(x$light == 0)) + 1 ]
>>          >          x
>>          >    }
>>          >
>>          >    do.call(rbind, by(d, d$day, f))
>>          >
>>          >    Hope this helps,
>>          >
>>          >    Rui Barradas
>>          >
>>          >    Em 15-07-2012 17:32, Santiago Guallar escreveu:
>>          >      > Hi,
>>          >      >
>>          >  > I have a dataset which contains several time records for
>>        a number
>>          >    of days, plus a variable (light) that allows to determine
>>        night time
>>          >    (lihgt= 0) and daytime (light> 0). I need to obtain get
>>        dusk time
>>          >    and dawn time for each day and place them in two columns.
>>          >      >
>>          >      > This is the starting point (d):
>>          >      > day time light
>>          >      > 1    1      20
>>          >      > 1    12    10
>>          >      > 1    11    6
>>          >      > 1    9      0
>>          >      > 1    6      0
>>          >      > 1    12    0
>>          >      > ...
>>          > > 30    8    0
>>          >      > 30    3    0
>>          >      > 30    8    0
>>          >      > 30    3    0
>>          >      > 30    8    8
>>          >      > 30    9    20
>>          >      >
>>          >      >
>>          >      > And this what I want to get:
>>          >      > day time light dusk dawn
>>          >      > 1    1      20    11    10
>>          >      > 1    12    10    11    10
>>          >      > 1    11    6      11    10
>>          >      > 1    9      0      11 10
>>          >      > 1    6      0      11    10
>>          >      > 1    12    0      11    10
>>          >      > ...
>>          >      > 30    8    0      9    5
>>          >      > 30    3    0      9    5
>>          >      > 30    8    0      9    5
>>          >      > 30    3    0      9    5
>>          >      > 30    8    8      9    5
>>          >      > 30    9    20    9    5
>>          >      >
>>          >      > This is the code for data frame d:
>>          >      > day= rep(1:30, each=10)
>>          >      > n= length(dia); x= c(1:24)
>>          >      > time= sample(x, 300, replace= T)
>>          >      > light= rep(c(20,10,6,0,0,0,0,0,8,20), 30)
>>          >      > d=data.frame(day,time,light)
>>          >      >
>>          >      > I'd need to impose a double condition like the next
>>        but if does
>>          >    not take more than one:
>>          >      > attach(d)
>>          >      > for (i in 1: n){
>>          >      > if (light[i-1]>2 & light[i]<2){
>>          >      > d$dusk<- time[i-1]
>>          >      > }
>>          >      > if (light[i-1]<2 & light[i]>2){
>>          >      > d$dawn<- time[i]
>>          >      > }
>>          >      > }
>>          >    > detach(d)
>>          >      > d
>>          >      >
>>          >      > Thank you for your help
>>          >      >    [[alternative HTML version deleted]]
>>          >      >
>>          >      >
>>          >      >
>>          >      > ______________________________________________
>>          >      > R-help@r-project.org <mailto:R-help@r-project.org>
>>        <mailto:R-help@r-project.org <mailto:R-help@r-project.org>>
>>        mailing list
>>          >      > https://stat.ethz.ch/mailman/listinfo/r-help
>>          >      > PLEASE do read the posting guide
>>          > http://www.R-project.org/posting-guide.html
>>        <http://www.r-project.org/posting-guide.html>
>>          >      > and provide commented, minimal, self-contained,
>>        reproducible code.
>>          >      >
>>          >
>>          >
>>          >
>>
>>
>>
>>
>>
>
>
>
>
	[[alternative HTML version deleted]]

