R help - May 2011 - Reading a large netCDF file using R

I got a netCDF file from a climate group and wanted to aggregate the data.
The file summary looks like this

library(ncdf)
nc=open.ncdf("NCEP_prec_1949_58.nc")
> nc
[1] "file NCEP_prec_1949_58.nc has 4 dimensions:"
[1] "Time   Size: 14608"
[1] "lat   Size: 99"
[1] "lon   Size: 199"
[1] "DateStrLen   Size: 20"
[1] "------------------------"
[1] "file NCEP_prec_1949_58.nc has 1 variables:"
[1] "float Prec[lon,lat,Time]  Longname:yearly accumulated precip
Missval:1e+30"

I tried to get the variable values using this command
> xx=get.var.ncdf(nc)
Error: cannot allocate vector of size 2.1 Gb

This file has six hourly data for the 199 x 99 points for 10 years. I wanted
to aggregate this data into a monthly scale. I tried used a simple code like
this 

for (i in 1:noofdays) {
	for (j in 0:3) {
		x= get.var.ncdf(nc,v1,start=c(1,1,(i+j)),count=c(199,99,1))
		temp_data_mat=temp_data_mat+x
	}
	
	for (x1 in 1:199) {
		for (x2 in 1:99) {
			data_mat_89_99[x1,x2,ctr]=temp_data_mat[x1,x2]
		}
	}
	ctr=ctr+1
	temp_data_mat=matrix(0,ncol=99,nrow=199)
}

I didnt think it worked... can u suggest me some other way ... I could not
use the start and count properly


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On Mon, May 9, 2011 at 6:29 PM, sulochandhungel
<sulochandhungel@gmail.com>wrote:
> I got a netCDF file from a climate group and wanted to aggregate the data.
> The file summary looks like this
> [...]
>
> I didnt think it worked... can u suggest me some other way ... I could not
> use the start and count properly

 Could you be a little more explicit? Why don't you think it worked?

In general, you seem to be using count and start correctly.

--Dave


-- 
David W. Pierce
Division of Climate, Atmospheric Science, and Physical Oceanography
Scripps Institution of Oceanography
(858) 534-8276 (voice)  /  (858) 534-8561 (fax)    dpierce@ucsd.edu

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