R/as.traj.r

In adehabitat: Analysis of Habitat Selection by Animals

"as.traj" <- function(id, xy, date, burst=id, ...)
{
    ## Verifications
    if (!is.data.frame(xy))
        stop("xy should be a data.frame")
    if (ncol(xy)!=2)
        stop("xy should have two columns")
    if (!inherits(date, "POSIXct"))
        stop("date should be of class \"POSIXct\"")
    id <- factor(id)
    burst <- factor(burst)
    if (!all(apply(table(id,burst)>0,2,sum)==1))
        stop("one burst level should belong to only one id level")

    ## Bases
    names(xy)<-c("x", "y")
    bas<-data.frame(id=id,
                    xy, date=date, burst=burst, ...)
    foo<-function(x) x[order(x$date),]
    li<-split(bas, bas$burst)
    nl <- unlist(lapply(li, nrow)) > 1
    li <- li[nl]
    if (any(!nl))
        warning(paste("At least two relocations are needed for a burst:\n",
                      sum(!nl), "circuits have been deleted"))
    li<-lapply(li, foo)


    ## Verification that no double dates
    foob<-function(x) {
        ind<-rep(0,nrow(x))
        for (i in 2:nrow(x)) {
            if ((as.numeric(x$date))[i]==(as.numeric(x$date))[i-1])
                ind[i]<-1
        }
        return(x[ind==0,])
    }

    ## output
    li<-lapply(li, foob)
    bas<-do.call("rbind", li)
    row.names(bas)<-as.character(1:nrow(bas))
    bas$id <- factor(bas$id)
    bas$burst <- factor(bas$burst)
    class(bas)<-c("traj", "data.frame")
    return(bas)
}