[R-sig-Geo] [FORGED] Modifying the length of a matrix variable

[Ben Tupper]

Hi,

It looks like you are accessing a NetCDF file or it's kin.  Like Rolf, I'm challenged to understand from your description what you are after.  Assuming you do indeed have a NetCDF file and are using the ncdf4 package, you can retrieve the first 90 layers as shown below using the varid, start and count arguments to ncvar_get().  Obviously, this is untested since your data isn't available to us.

library(ncdf4)
filename = "/path/to/foo.nc"
ncObject <- nc_open(filename)
m <- ncvar_get(ncObject varid = "onedaymax", start = c(1,1,1), count = c(-1,-1, 90))
nc_close(ncObject)


See more details and examples here... https://www.rdocumentation.org/packages/ncdf4/versions/1.16.1/topics/ncvar_get


You might also consider using the raster package which will retrieve multilayer georeferenced rasters for you from the same NetCDF file.

library(raster)
B <- brick(filename, varname = "onedaymax")
B <- B[[-c(91:95)]]    # <- drop the last layers 91, 92, ...95

See the docs here... https://www.rdocumentation.org/packages/raster/versions/2.8-19/topics/brick

Cheers,
Ben

> On Mar 30, 2019, at 7:30 PM, rain1290--- via R-sig-Geo <r-sig-geo using r-project.org> wrote:
> 
> Yes, I reproduced the example above and it works just fine (and is what I want!!), but I cannot see why it does not work with my data, as it is a 3-dimensional array (latitude, longitude and time). 
> This is what comes from print(Model4):
> 3 variables (excluding dimension variables):
>        double onedaymax[lon,lat,time]   (Contiguous storage)  
>            units: mm/day
>        double fivedaymax[lon,lat,time]   (Contiguous storage)  
>            units: mm/day
>        short Year[time]   (Contiguous storage)  
> 
>     3 dimensions:
>        time  Size:95
>        lat  Size:64
>            units: degree North
>        lon  Size:128
>            units: degree East
> I reviewed it over and over again, but I cannot see why this would not work?
> Thanks, 
> 
> 
> -----Original Message-----
> From: Rolf Turner <r.turner using auckland.ac.nz>
> To: rain1290 <rain1290 using aim.com>
> Cc: r-sig-geo <r-sig-geo using r-project.org>
> Sent: Sat, Mar 30, 2019 6:49 pm
> Subject: Re: [FORGED] [R-sig-Geo] Modifying the length of a matrix variable
> 
> 
> On 31/03/19 11:14 AM, rain1290 using aim.com wrote:
> 
>> Hi Rolf (and others),
>> 
>> I tried your suggestion, but when I used dim(Model4.chopped), it still 
>> shows 95 layers, as shown below:
>> 
>> 8192    95
>> 
>> I also find that the total number of cells is rather low for that many 
>> layers. I started with 778240 cells over 95 layers.
> 
> Well then you're doing something wrong, or there is something that you 
> haven't told us.
> 
> E.g.:
>> junk <- array(runif(64*128*95),dim=c(64,128,95))
>> junk.chopped <- junk[,,1:90]
>> dim(junk)
>> [1]  64 128  95
>> dim(junk.chopped)
>> [1]  64 128  90
> 
> Perhaps Model.4 has some structure other than that of an array. 
> (Originally you said it was a matrix.)
> 
> You really need to get your terminology and ideas *clear* in order to 
> have any hope of receiving useful advice.
> 
> I have no idea what you are on about in respect of "the number of 
> cells".  My mind-reading machine is in the repair shop.  I strongly 
> suspect that your thoughts are confused.
> 
> cheers,
> 
> Rolf
> 
> -- 
> Honorary Research Fellow
> Department of Statistics
> University of Auckland
> Phone: +64-9-373-7599 ext. 88276
> 
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> 
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Ben Tupper
Bigelow Laboratory for Ocean Sciences
60 Bigelow Drive, P.O. Box 380
East Boothbay, Maine 04544
http://www.bigelow.org

Ecological Forecasting: https://eco.bigelow.org/