[R-sig-Geo] raster::clump not working?

[Ben Tupper]

Hi,

I think it is actually correct - there is only one 'clump' of connected cells.  In raster clumps are separated from other clumps by backgound (0 or NA).  In your example there is no background anywhere so there is just one clump. 

You can see the difference if you divide x in to halves with a row of NAs.  Note that limited spatial extent so the clumping doesn't wrap around the globe which it will for [-180, 180].

r <- raster(ncols=36, nrows=18, xmn = 0, xmx = 36, ymn = 0, ymx = 18)
x <- init(r, fun='cell')
 
x[9,1:36] <- NA
y <- clump(x)
y
# class       : RasterLayer 
# dimensions  : 18, 36, 648  (nrow, ncol, ncell)
# resolution  : 1, 1  (x, y)
# extent      : 0, 36, 0, 18  (xmin, xmax, ymin, ymax)
# coord. ref. : +proj=longlat +datum=WGS84 +ellps=WGS84 +towgs84=0,0,0 
# data source : in memory
# names       : clumps 
# values      : 1, 2  (min, max)

x[1:18, 18] <- NA
y
# class       : RasterLayer 
# dimensions  : 18, 36, 648  (nrow, ncol, ncell)
# resolution  : 1, 1  (x, y)
# extent      : 0, 36, 0, 18  (xmin, xmax, ymin, ymax)
# coord. ref. : +proj=longlat +datum=WGS84 +ellps=WGS84 +towgs84=0,0,0 
# data source : in memory
# names       : clumps 
# values      : 1, 4  (min, max)


Cheers,
Ben


> On May 25, 2018, at 6:00 AM, João Carreiras <jmbcarreiras using gmail.com> wrote:
> 
> Hi!
> 
> I've been trying to run the clump command but the output is consistently a
> raster with values == 1. Please find below an example.
> 
> I'm sure I'm doing something stupid. However, the command is really
> straightforward and I can't seem to identify what the problem might be.
> 
> Any help really appreciated.
> Thanks
> Joao
> 
> r <- raster(ncols=36, nrows=18)
> x <- init(r, fun='cell')
> x
> class       : RasterLayer
> dimensions  : 18, 36, 648  (nrow, ncol, ncell)
> resolution  : 10, 10  (x, y)
> extent      : -180, 180, -90, 90  (xmin, xmax, ymin, ymax)
> coord. ref. : +proj=longlat +datum=WGS84 +ellps=WGS84 +towgs84=0,0,0
> data source : in memory
> names       : layer
> values      : 1, 648  (min, max)
> a <- clump(x)
> a
> class       : RasterLayer
> dimensions  : 18, 36, 648  (nrow, ncol, ncell)
> resolution  : 10, 10  (x, y)
> extent      : -180, 180, -90, 90  (xmin, xmax, ymin, ymax)
> coord. ref. : +proj=longlat +datum=WGS84 +ellps=WGS84 +towgs84=0,0,0
> data source : in memory
> names       : clumps
> values      : 1, 1  (min, max)
> 
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Ben Tupper
Bigelow Laboratory for Ocean Sciences
60 Bigelow Drive, P.O. Box 380
East Boothbay, Maine 04544
http://www.bigelow.org

Ecological Forecasting: https://eco.bigelow.org/






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