[GRASS-stats] Load data multiple data from grass to R

[Roger Bivand]

On Thu, 22 Nov 2007, Jarek Jasiewicz wrote:

> Roger Bivand wrote:
>>  On Wed, 21 Nov 2007, Jarek Jasiewicz wrote:
>> 
>> >  I'd like to write R sript to read more rasters from grass to R and 
>> >  writeh them to objects with unique
>> > 
>> >  what I try to do:
>> > 
>> >  system("g.mlist type=rast pattern=a_* >tmp_file")
>> >  k=c(scan("temp_file, what="string")) //maybe is simpler way
>> > 
>> >  for (i in k) {
>> >  here_I_need_obect_with_unique_name=readRAST6(i, paste(i))
>>> }
>> >  operations_on_obiects
>>
>>  Could you use the fact that the first argument to readRAST6() can be a
>>  character vector of raster layer names? If k is such a character vector,
>>  you could try readRAST6(k). The second argument is a logical vector, not
>>  vname= as you seem to think - that is in writeRAST6().
>>
>>  Hope this helps,
>>
>>  Roger
>>
>>  obiect <-readRAST6(k)
> well maybe presented problem not enough clear
> First - there is en mistake in code i typed
> shuoud be:
>
> for (i in k) {
> here_I_need_obect_with_unique_name=readRAST6(i)
> }
>
> but in that way I recive obiect which every iteration will be overwritten by 
> nex raster map. At the end I will have obiect with last raster map in string 
> vector
>
> How to preserve obiect created in the loop and control its name?
> I think about something like this (for example) in the loop ??

What I suggested was putting all the rasters into the same object - their 
names become the column names of the object. Since the current region is 
respected, they will be conformal. If you want multiple objects, use 
assign() which takes a character string as the name if the object being 
assigned to, but watch the scoping if you are doing this in a function.

Roger

>
> ob_a=readRAST6("a")
> ob_b=readRAST6("b")
> ob_c=readRAST6("c")
> ...
> ob_z=readRAST6("z")
>
> if I use this
>
> obiect <-readRAST6(k)
>
> there will be the problem with converting every layer (I mean: 
> "obiect at data$raster_name" i SpGridDataFrame) in multilayer SpGridDataFrame to 
> "im" class obiect
>
> In general it is the problem how to control names of obiect if in the loop we 
> need to create more than one obiect
>
> Hope I presented it clear
>
> greetings
> Jarek
>
>

-- 
Roger Bivand
Economic Geography Section, Department of Economics, Norwegian School of
Economics and Business Administration, Helleveien 30, N-5045 Bergen,
Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43
e-mail: Roger.Bivand at nhh.no