On Feb 11, 2011, at 5:11 AM, Xavier Hoenner wrote:
Dear R-users,
Im currently trying to extract the value of a slot (area) but cant
find out how to do that.
Generally the authors of S4 method provide extractor functions, so the
first question would be what functions were used to create the object.
Fortunately there are big hints in the first line of str() results.
The documentation for package sp says there is a summary method for
that class as well as a "[" method. Those results may offer avenues
for progresss
These might yield objects that could be further used:
area(overlperc[1]) or polygons(overlperc) but my efforts at finding an
area-extractor in the sp vignettes and RSiteSearch were not fulfilled.
A brute force method is to use the primitive S4 extractor function "@"
to traverse the tree:
So you might try either of these:
polygons(overlperc)[[1]]@area #didn't work on the test object I made
with one of the examples in pkg::sp
This appears more likely to succeed:
overlperc@polygons[[1]]@area
There's also a specific mailing list for geospatial stats.
--
David.
str(overlperc)
List of 1
$ :Formal class 'SpatialPolygons' [package "sp"] with 4 slots
.. ..@ polygons :List of 1
.. .. ..$ :Formal class 'Polygons' [package "sp"] with 5 slots
.. .. .. .. ..@ Polygons :List of 1
.. .. .. .. .. ..$ :Formal class 'Polygon' [package "sp"] with 5
slots
.. .. .. .. .. .. .. ..@ labpt : num [1:2] 709374 -1507888
.. .. .. .. .. .. .. ..@ area : num 11542604
.. .. .. .. .. .. .. ..@ hole : logi FALSE
.. .. .. .. .. .. .. ..@ ringDir: int 1
.. .. .. .. .. .. .. ..@ coords : num [1:23, 1:2] 706840 706657
706840 707294 707585 ...
.. .. .. .. .. .. .. .. ..- attr(*, "dimnames")=List of 2
.. .. .. .. .. .. .. .. .. ..$ : chr [1:23] "1" "2" "3" "4" ...
.. .. .. .. .. .. .. .. .. ..$ : chr [1:2] "x" "y"
.. .. .. .. ..@ plotOrder: int 1
.. .. .. .. ..@ labpt : num [1:2] 709374 -1507888
.. .. .. .. ..@ ID : chr "1"
.. .. .. .. ..@ area : num 11542604
.. ..@ plotOrder : int 1
.. ..@ bbox : num [1:2, 1:2] 706657 -1509411 711710 -1506189
.. .. ..- attr(*, "dimnames")=List of 2
.. .. .. ..$ : chr [1:2] "x" "y"
.. .. .. ..$ : chr [1:2] "min" "max"
.. ..@ proj4string:Formal class 'CRS' [package "sp"] with 1 slots
.. .. .. ..@ projargs: chr NA
Id like to extract the area value so as to be able to use this
value for further analysis. Heres below what I get when I only type
the name of the object:
overlperc
[[1]]
An object of class "SpatialPolygons"
Slot "polygons":
[[1]]
An object of class "Polygons"
Slot "Polygons":
[[1]]
An object of class "Polygon"
Slot "labpt":
[1] 709374 -1507888
Slot "area":
[1] 11542604
Slot "hole":
[1] FALSE
Slot "ringDir":
[1] 1
Slot "coords":
x y
1 706839.8 -1508654
2 706657.2 -1508029
3 706839.8 -1507634
4 707293.6 -1507284
5 707584.7 -1507174
6 708329.6 -1506851
7 709013.3 -1506539
8 709074.5 -1506513
9 709819.5 -1506189
10 710564.4 -1506289
11 711021.1 -1506539
12 711309.3 -1506769
13 711642.0 -1507284
14 711709.8 -1508029
15 711309.3 -1508690
16 711246.4 -1508774
17 710564.4 -1509347
18 709819.5 -1509411
19 709074.5 -1509277
20 708329.6 -1509072
21 707584.7 -1509039
22 706927.4 -1508774
23 706839.8 -1508654
Slot "plotOrder":
[1] 1
Slot "labpt":
[1] 709374 -1507888
Slot "ID":
[1] "1"
Slot "area":
[1] 11542604
Slot "plotOrder":
[1] 1
Slot "bbox":
min max
x 706657.2 711709.8
y -1509411.3 -1506189.0
Slot "proj4string":
CRS arguments: NA
Im stuck and spent more or less the whole afternoon online trying
to find a solution to my problem but I couldnt find anything. I
look forward to hear from some of you. Thanks in advance for your
kind help.
Have a good weekend.
Cheers
Xavier
Xavier Hoenner
PhD Student
Nesting Ecology, Migrations and Diving Behaviour of Hawksbill Turtles
School of Environmental Research, Charles Darwin University
Darwin, NT 0909
Ph: (08)8946.7721
email:[email protected]
[[alternative HTML version deleted]]
______________________________________________
[email protected] mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
David Winsemius, MD
West Hartford, CT
______________________________________________
[email protected] mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
