[R-sig-eco] Extract from class object ltraj.

[Sarah Goslee]

Hi Dylann,

On Tue, Jun 11, 2013 at 11:36 AM, Dylann Kersusan
<kersusan.dylann at gmail.com> wrote:
> Hi everyone,
>
> I am working on class object "ltraj" mainly using the package Adehabitat HT
> and LT.
> Is there a way to extract from this class object the distances between
> relocations ("dist")? I am pretty sure that it is possible and it has to be
> easy, but I am probably missing something. I tried the following though:
>
> ltrj.obj <- as.ltraj(xy, date = dates, id = data$name, infolocs =
> data.frame(idnr = data$idnr))
> str(ltrj.obj)
>
> List of 1
>  $ :'data.frame':       1328 obs. of  10 variables:
>   ..$ x        : int [1:1328] 1559670 1559665 1559687 1559695 1559695
> 1559686 1559687 1559674 1559648 1559666 ...
>   ..$ y        : int [1:1328] 7448557 7448603 7448611 7448592 7448594
> 7448598 7448599 7448568 7448522 7448532 ...
>   ..$ date     : POSIXct[1:1328], format: "2009-05-15 00:00:54"
> "2009-05-15 00:30:21" "2009-05-15 01:00:35" ...
>   ..$ dx       : int [1:1328] -5 22 8 0 -9 1 -13 -26 18 2 ...
>   ..$ dy       : int [1:1328] 46 8 -19 2 4 1 -31 -46 10 -2 ...
>   ..$ dist     : num [1:1328] 46.27 23.41 20.62 2 9.85 ...
>   ..$ dt       : num [1:1328] 1767 1814 1842 1766 1799 ...
>
>
> distance <- ltrj.obj$data.frame$dist

You're conflating class and name.

A ltraj object is a list of data frames. Your list happens to only
have one data frame, but there can be many. That data frame has 10
columns, and str() gives the names, as would
names(ltrj.obj[[1]])

length(ltrj.obj) # should be 1, based on the output you showed

ltrj.obj[[1]]$dist

will give you what you're looking for, as would

ltrj.obj[[1]][['dist']]

-- 
Sarah Goslee
http://www.functionaldiversity.org