create netcdf in R with multiples variables - r

Question

I want to create a netcdf with 11 or more different variables. For that I was trying to write it within a loop, but it is not working. My code would be something like that:
#Defining names and dimensions
nam_cwt <- c("N","NE","E","SE","S","SW","W","NW","C","A","U") #number of variables
CWTvar <- paste("var_",nam_cwt,sep="")
data_cwt <- list()
mat_cwt <- array()
dimX <- dim.def.ncdf("longitude", "degrees_east", Longvector)
dimY <- dim.def.ncdf("latitude", "degrees_north", Latvector)
dimT <- dim.def.ncdf("time","days since 1961-01-01",1:length(my.date), unlim=TRUE)
missval <- -999
#Creating and filling the netcdf file
for (i in 1:length(nam_cwt)){
#Getting every matrix of elements
data_cwt <- lapply(cwt_out,function(x) x[[1]][[i]][[2]])
dmatrix <- unlist(data_cwt)
mat_cwt <- array(dmatrix,dim=c(144,length(my.date),25))
tmat_cwt <- aperm(mat_cwt,c(1,3,2))
CWTvar[[i]] <- var.def.ncdf(nam_cwt[i],"days",list(dimX,dimY,dimT), ,missval,longname=nam_cwt[i])
ncfile <- create.ncdf("nctypes.nc",CWTvar)
put.var.ncdf(ncfile,CWTvar[i],tmat_cwt)
}
The problem is that I am not sure if I should use var.add.ncdf (instead put.var.ncdf)..
any idea about that???
How can I create and write the file within the loop??
Any help will be helpful!

Answer 1

Here's how I would do this: create a netcdf file first with one of the variables, then add and fill the others in a loop.
library(ncdf)
#Defining names and dimensions
nam_cwt <- c("N","NE","E","SE","S","SW","W","NW","C","A","U") #number of variables
CWTvar <- paste("var_",nam_cwt,sep="")
# values and length of dimensions
Longvector = -180:180
Latvector = -90:90
Datevector = 1:10
x= length(Longvector)
y= length(Latvector)
z= length(Datevector)
# define dimensions
dimX <- dim.def.ncdf("longitude", "degrees_east", Longvector)
dimY <- dim.def.ncdf("latitude", "degrees_north", Latvector)
dimT <- dim.def.ncdf("time","days since 1961-01-01",1:length(Datevector), unlim=TRUE)
# set missing value
missval <- -9999
# create the file with first variable so dimensions are set
CWTvar1 <- var.def.ncdf(name=nam_cwt[1],"days",list(dimX,dimY,dimT), missval=missval)
ncfile <- create.ncdf("nctypes.nc",vars=CWTvar1)
# open newly created file for writing data
mync = open.ncdf(con='nctypes.nc', write=T)
# create some data for first variable
mydata = array(data=runif(n=x*y*z, min=0, max=10), dim=c(x,y,z))
# add data to ncdf file
put.var.ncdf(nc=mync, varid='N', vals=mydata)
# now add all other variables with the same dimensions
for (i in 2:length(nam_cwt)){
# generate new data
mydata = array(data=runif(n=x*y*z, min=0, max=10)*i, dim=c(x,y,z))
# create new variable
CWTvar <- var.def.ncdf(name=nam_cwt[i],"days",list(dimX,dimY,dimT) ,missval=missval)
# add new variable to existing file
mync = var.add.ncdf(nc=mync, v=CWTvar)
# add data to variable in file
put.var.ncdf(nc=mync,varid=CWTvar$name,vals=mydata)
}
close.ncdf(mync)
# check file
newnc = open.ncdf(con='nctypes.nc')
par(mfrow=c(4,3))
for (i in 1:length(nam_cwt)){
zz = get.var.ncdf(newnc, varid=nam_cwt[i])
image(x=Longvector, y=Latvector, z=zz[,,1])
}
close.ncdf(newnc)