No, apparently it is still a brick:

> class(b)
[1] "RasterBrick"
attr(,"package")
[1] "raster"


Here is a minimum (not)-working example, based on this post, which seems to
be having similar problems:
http://r-sig-geo.2731867.n2.nabble.com/Subset-a-Raster-object-read-from-a-4D-NetCDF-file-td7586200.html

Example follows:
> library(raster)
Loading required package: sp
> b <- brick('
http://www.esrl.noaa.gov/psd/thredds/dodsC/Datasets/godas/pottmp.2013.nc',
lvar=3, level=1, varname='pottmp')
> b
class       : RasterBrick
dimensions  : 418, 360, 150480, 12  (nrow, ncol, ncell, nlayers)
resolution  : 1, 0.3333309  (x, y)
extent      : 0, 360, -74.66667, 64.66567  (xmin, xmax, ymin, ymax)
coord. ref. : +proj=longlat +datum=WGS84
data source :
http://www.esrl.noaa.gov/psd/thredds/dodsC/Datasets/godas/pottmp.2013.nc
names       : X2013.01.01, X2013.02.01, X2013.03.01, X2013.04.01,
X2013.05.01, X2013.06.01, X2013.07.01, X2013.08.01, X2013.09.01,
X2013.10.01, X2013.11.01, X2013.12.01
Date        : 2013-01-01, 2013-02-01, 2013-03-01, 2013-04-01, 2013-05-01,
2013-06-01, 2013-07-01, 2013-08-01, 2013-09-01, 2013-10-01, 2013-11-01,
2013-12-01
varname     : pottmp
level       : 1

> dropLayer(b,1)
Error in (function (classes, fdef, mtable)  :
  unable to find an inherited method for function ‘extent’ for signature
‘"character"’
In addition: Warning message:
In .stackCDF(x, varname = varname, bands = bands) :
  pottmp has 4 dimensions, I am using the last one
>



On 29 July 2014 13:24, Michael Sumner <mdsumner@gmail.com> wrote:

> Are you sure that your "b" is still really a RasterBrick? That message
> comes if you give the functions character:
>
> library(raster)
> dropLayer("sometext", 1)
> Error in (function (classes, fdef, mtable)  :
>   unable to find an inherited method for function ‘dropLayer’ for
> signature ‘"character"’
>
> (Basically because the functions are all generics, they scans through
> available methods and tells you it can't find one for "character").
>
> It works for me, see contrived example below that I had on hand due to
> obscure testing many years ago.
> (There is warning related to subsetting a linked-4D file, but that
> seems harmless).
>
> But, also try selecting only the bands you want at read time (or even
> just use a stack), so
>
> b <- brick("/blah/blah/ncep_07c_tho_all_1948-2010.mon.nc", level = 3,
> band = 1:5)
>
> Cheers, Mike.
>
> ## create a 4D NetCDF file in R
> ## load NetCDF package
> library(RNetCDF)
> ## generate 4D data - 1:N
> dims <- c(2, 3, 2, 2)
> a <- array(data = 1:prod(dims), dim = dims)
>
> ## create NetCDF file
> nc <- create.nc("test-1.nc")
> ## coordinate values for NetCDF (to test transform and band metadata)
> x <- seq(0, 5, length = dim(a)[1])
> y <- seq(0, 2, length = dim(a)[2])
> c3 <- seq(0, 1, length = dim(a)[3])
> c4 <- seq(0, 1, length = dim(a)[4])
>
> ## dimensions
> dim.def.nc(nc, "x", length(x))
> dim.def.nc(nc, "y", length(y))
> dim.def.nc(nc, "c3", length(c3))
> dim.def.nc(nc, "c4", length(c4))
>
> ## variables
> var.def.nc(nc, "a", "NC_DOUBLE", c(0, 1, 2, 3))
> var.def.nc(nc, "x", "NC_DOUBLE", 0)
> var.def.nc(nc, "y", "NC_DOUBLE", 1)
> var.def.nc(nc, "c3", "NC_DOUBLE", 2)
> var.def.nc(nc, "c4", "NC_DOUBLE", 3)
> ## write the data (all at once, no start/count)
> var.put.nc(nc, "a", a)
> var.put.nc(nc, "x", x)
> var.put.nc(nc, "y", y)
> var.put.nc(nc, "c3", c3)
> var.put.nc(nc, "c4", c4)
> ## finish up
> close.nc(nc)
>
> library(raster)
> b <- brick("test-1.nc", level = 2)
> nlevels(b)
> dropLayer(b, 1)
> class       : RasterLayer
> band        : 2  (of  2  bands)
> dimensions  : 3, 2, 6  (nrow, ncol, ncell)
> resolution  : 5, 1  (x, y)
> extent      : -2.5, 7.5, -0.5, 2.5  (xmin, xmax, ymin, ymax)
> coord. ref. : NA
> data source : C:\temp\test-1.nc
> names       : X1
> z-value     : 1
> zvar        : a
> level       : 1
>
> Warning message:
> In .rasterObjectFromCDF(x, type = objecttype, band = band, ...) :
>   "level" set to 1 (there are 2 levels)
>
>
> On Tue, Jul 29, 2014 at 7:43 PM, Mark Payne <markpayneatwork@gmail.com>
> wrote:
> > Hi,
> >
> > I have a 4D climate model output that I am trying to work with via
> raster,
> > and that is unfortunately giving problems. I create the object as a
> brick:
> >
> >> b
> > class       : RasterBrick
> > dimensions  : 220, 254, 55880, 756  (nrow, ncol, ncell, nlayers)
> > resolution  : 1, 1  (x, y)
> > extent      : 0.5, 254.5, 0.5, 220.5  (xmin, xmax, ymin, ymax)
> > coord. ref. : +proj=longlat +datum=WGS84
> > data source : /home/mpayne/Documents/NACLIM/
> > ncep_07c_tho_all_1948-2010.mon.nc
> > names       : X19480131, X19480229, X19480331, X19480430, X19480531,
> > X19480630, X19480731, X19480831, X19480930, X19481031, X19481130,
> > X19481231, X19490131, X19490228, X19490331, ...
> > z-value     : 19480131, 20101231 (min, max)
> > varname     : var2
> > level       : 3
> >
> > But I would like to drop a lot of the layers, so I try:
> >
> >> dropLayer(b,1:5)
> > Error in (function (classes, fdef, mtable)  :
> >   unable to find an inherited method for function ‘extent’ for signature
> > ‘"character"’
> >>
> >
> > And get a rather strange error.... Trying subset instead:
> >
> >> subset(b,1:5)
> > Error in (function (classes, fdef, mtable)  :
> >   unable to find an inherited method for function ‘extent’ for signature
> > ‘"character"’
> >>
> > Gives the same error. I'm assuming that this is related to the 4D nature
> of
> > the data, as I can't reproduce it elsewise, e.g. using the examples...
> Any
> > ideas?
> >
> > Best wishes,
> >
> > Mark
> >
> >         [[alternative HTML version deleted]]
> >
> >
> > _______________________________________________
> > R-sig-Geo mailing list
> > R-sig-Geo@r-project.org
> > https://stat.ethz.ch/mailman/listinfo/r-sig-geo
> >
>
>
>
> --
> Michael Sumner
> Software and Database Engineer
> Australian Antarctic Division
> Hobart, Australia
> e-mail: mdsumner@gmail.com
>

	[[alternative HTML version deleted]]

