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

[Sarah Goslee]

Hi,

On Tue, Jun 11, 2013 at 12:55 PM, Dylann Kersusan
<kersusan.dylann at gmail.com> wrote:
> Thanks a lot. It works perfectly fine! Though I don't know how to arrange
> that into a column, I shall find something not too time consuming.

The code I provided extracts the distances as a vector. What are you
trying to do with them?

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

will return a one-column data frame.

You might like to take some time to read the intro to R documentation,
particularly the parts about subsetting and the difference between [
and [[ to understand why.

Sarah

>
> 2013/6/11 Sarah Goslee <sarah.goslee at gmail.com>
>>
>> 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