raster::clump not working?

Dear Ben,

Thank you for your prompt reply.

Now I see what clump does. I just thought clump would give the same
result as ArcGIS "Region Group". I need some command to assign a
different value to each patch. And by patch I mean contiguous pixels
having the same value, so that in this (absurd) example I would get
648 patches.

Take care
Joao

On 25 May 2018 at 11:35, Ben Tupper <btupper at bigelow.org> wrote:

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, Jo?o Carreiras <jmbcarreiras at 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)