R/traj2sldf.r

In adehabitat: Analysis of Habitat Selection by Animals

"traj2sldf" <- function(tr, byid = FALSE)
{
    ## Verifications
    if (!inherits(tr, "traj"))
        stop("tr should be of class \"traj\"")

    ## Conversion to data frame
    class(tr) <- "data.frame"

    ## Conversion as list of Lines
    lixy <- lapply(split(tr[,c("x","y")], tr$burst),
                   function(x) Line(as.matrix(x)))
    id <- unlist(lapply(split(tr$id, tr$burst), function(x) x[1]))
    bu <- unlist(lapply(split(tr$burst, tr$burst), function(x) x[1]))


    if (byid) {

        ## If one line per ID -> SpatialLines
        lev <- levels(factor(id))
        re1 <- lapply(lev, function(x) Lines(lixy[id==x], ID=x))
        res <- SpatialLines(re1)
        df <- data.frame(id=lev)
    } else {

        ## If one line per ID -> SpatialLines
        res <- lapply(1:length(lixy),
                      function(i) Lines(list(lixy[[i]]), ID=names(lixy)[i]))
        res <- SpatialLines(res)
        df <- data.frame(id=id, burst=bu)
    }

    ## Output
    res <- SpatialLinesDataFrame(res, data=df)
    return(res)
}