[R-sig-eco] Working with trajectories: ltraj.

[Clement Calenge]

[snip]
> I am trying to select only a part of the trajectory stored in this ltraj
> class object, following an example from Calenge in the package
> 'adehabitatLT':
>
> lim <- as.POSIXct(strptime(c("28/05/2010 02:00:40", "30/06/2010 02:00:41"),
> "%d/%m/%Y %H:%M:%S"))
> ltrj.bis <- gdltraj(ltrj.obj, min=lim[1], max=lim[2], type="POSIXct" )
>
> but for some reasons it does not work properly. I got this error message
> that I do not understand:
>
> Error in `[.default`(res, , names(res) %in% which, drop = FALSE) :
>    number of dimensions incorrect
>
>
> Anyone has an idea about why it doesn't work?

You have identified a bug in the function gdltraj. I have corrected this 
bug and uploaded a new version of the package to CRAN. It will be 
available soon. Meanwhile, you can use this function instead:

gdltraj <- function (x, min, max, type = c("POSIXct", "sec", "min", "hour",
     "mday", "mon", "year", "wday", "yday"))
{
     if (!inherits(x, "ltraj"))
         stop("x should be of class \"ltraj\"")
     if (!attr(x, "typeII"))
         stop("x should be of type II (time recorded)")
     type <- match.arg(type)
     if (type == "POSIXct") {
         x <- lapply(x, function(y) {
             infol <- attr(y, "infolocs")
             if (!is.null(infol))
                 infol <- infol[(y$date > min) & (y$date < max),
                   , drop=FALSE]
             y <- y[(y$date > min) & (y$date < max), ]
             if (!is.null(infol))
                 attr(y, "infolocs") <- infol
             return(y)
         })
     }
     else {
         x <- lapply(x, function(y) {
             da <- as.POSIXlt(y$date)[[type]]
             infol <- attr(y, "infolocs")
             if (!is.null(infol))
                 infol <- infol[(da >= min) & (da < max), ,drop=FALSE]
             y <- y[(da >= min) & (da < max), ]
             if (!is.null(infol))
                 attr(y, "infolocs") <- infol
             return(y)
         })
     }
     if (all(sapply(x, nrow) == 0))
         stop("No relocations within the specified interval")
     x[sapply(x, nrow) == 0] <- NULL
     class(x) <- c("ltraj", "list")
     attr(x, "typeII") <- TRUE
     attr(x, "regular") <- is.regular(x)
     x <- rec(x)
     return(x)
}

HTH

Clément Calenge

-- 
Clément CALENGE
Cellule d'appui à l'analyse de données
Direction des Etudes et de la Recherche
Office national de la chasse et de la faune sauvage
Saint Benoist - 78610 Auffargis
tel. (33) 01.30.46.54.14