My data frame shows changes on the variable act which records the consecutive
duration (in seconds) of two states (wet-dry) over a few days for
several?individuals (identified by Ring). Since I want to work with daytime
(i.e. from dawn till dusk) and night time (i.e. from dusk till next dawn), I
have to split act in two: from time[i] till dusk and from dusk until time[i+1],
and from time[k] till dawn and from dawn until time[k+1].
Example:
ith row: 01-01-2000 20:55:00 act= 360 seconds
i+1th row: 01-01-2000 21:01:00 act= 30 seconds # say that dusk= 21:00
i+2th row: 01-01-2000 21:01:30 act= 30 seconds
.
.
.
My goal is to get:
ith row: 01-01-2000 20:55:00 act= 300 seconds # modified row
i+1th row: 01-01-2000 21:00:00 act= 60 seconds # new row
i+2th row: 01-01-2000 00:01:00 act= 30 seconds # previously row i+1th
i+3th row: 01-01-2000 00:01:30 act= 30 seconds # previously row i+2th
.
.
.
I attach a dput with a selection of my data. Here's a piece of code that I
am trying to run only for the daytime/night time change:
? xandn <- ddply( xan, .(Ring), function(df1){
? # ?ndex of daytime/night time changes
? ind <- c( FALSE,?diff( as.POSIXlt( df1$timepos, df1$dusk ) ) > 0?)
? add <- df1[ind,]
? add$timepos <- add$timepos - add$dusk
? # append and arrange rows
? df1 <- rbind( df1, add )
? df1 <- df1[order(df1$timepos),]
? # recalculation of act
? df1$act2 <- c( diff( as.numeric(df1$timepos) ), NA )
? df1} )
I get the following error message:
"Error in diff(as.POSIXlt(df1$timepos, df1$dusk)): error in evaluating the
argument 'x' in selecting a method for function 'diff': Error in
as.POSIXlt.POSIXct?(df1$timepos, df1$dusk): ? invalid 'tz' value"
Thank you for your hep,
Santi
