I have a netcdf file that contains 79 variables, and for each variable there are 365 bands (one for each day of the year). I want to read all bands of one variable (i.e., a raster with 365 ayers). With the 'raster' package this would work as follows:
dailyvalues <- brick('GLOBAL_2010_day.nc', varname ='WDEP_PREC')
Result is a RasterBrick with 365 layers:
> dailyvalues
class : RasterBrick
dimensions : 180, 360, 64800, 365 (nrow, ncol, ncell, nlayers)
resolution : 1, 1 (x, y)
extent : -180, 180, -90, 90 (xmin, xmax, ymin, ymax)
crs : +proj=longlat +datum=WGS84 +no_defs
source : GLOBAL_2010_day.nc
names : X2010.01.01, X2010.01.02, X2010.01.03, X2010.01.04, X2010.01.05, X2010.01.06, X2010.01.07, X2010.01.08, X2010.01.09, X2010.01.10, X2010.01.11, X2010.01.12, X2010.01.13, X2010.01.14, X2010.01.15, ...
Date : 2010-01-01, 2010-12-31 (min, max)
varname : WDEP_PREC
But I haven't suceeded to do this with the 'terra' package. I tried
dailyvalues <- rast('GLOBAL_2010_day.nc')
> dailyvalues
class : SpatRaster
dimensions : 180, 360, 28835 (nrow, ncol, nlyr)
resolution : 1, 1 (x, y)
extent : -180, 180, -90, 90 (xmin, xmax, ymin, ymax)
coord. ref. : +proj=longlat +datum=WGS84 +no_defs
sources : GLOBAL_2010_day.nc:WDEP_PREC (365 layers)
GLOBAL_2010_day.nc:WDEP_SOX (365 layers)
GLOBAL_2010_day.nc:WDEP_OXN (365 layers)
... and 76 more source(s)
varnames : WDEP_PREC (WDEP_PREC)
WDEP_SOX (WDEP_SOX)
WDEP_OXN (WDEP_OXN)
...
names : WDEP_PREC_1, WDEP_PREC_2, WDEP_PREC_3, WDEP_PREC_4, WDEP_PREC_5, WDEP_PREC_6, ...
unit : mm, mm, mm, mm, mm, mm, ...
time : 2010-01-01 18:00:00 to 2010-12-31 12:00:00
The resulting SpatRaster has 79 'sources', but what is the syntax to use if I want to extract one 'source'? Adding varname = 'WDEP_PREC' in the rast function doesn't work. I tried dailyvalues$... but that calls single layers only (as listed under 'names').
You should be able to do (as @dww says)
dailyvalues = rast("GLOBAL_2010_day.nc", subds="WDEP_PREC")
Or you can make a SpatRasterDataset
x = sds("GLOBAL_2010_day.nc")
And then extract the sub-dataset you want with
r <- x["WDEP_PREC"]
or
r <- x[1]
Furthermore, you can do
r <- rast('NETCDF:"GLOBAL_2010_day.nc:WDEP_PREC":WDEP_PREC')
(for the above to work you may need to add the path to the filename, or set your working directory to where it is)