Hello all,

I've just started working with gridded data in R, mostly in using the
"rworldmap" package.

So far I have been able to make ASCIIgrid files of global datasets that I
imported into R as simple matrices (ex. 360x180 matrix with data values
corresponding to each of the 1x1 grid), and draw them with functions
included in "rworldmap".

My problem now is in manipulating parts of these datasets, specifically with
regards to country.

For example, from the global matrix I want to subset just the grids that
belong to China and multiply a factor to those Chinese grids, or maybe make
them all 0s.

Selecting all the grids that belong to a country seems straightforward in
theory, but being the novice that I am, I can't figure out an effective way
to do this.

I've also been thinking that I should probably switch over my simple
matrices to sp dataframes, so that the spatial aspects of my dataset can be
better handled within R, but so far have been hesitant to do so because the
benefits of such a change have not been apparent.


Can I get some suggestions or help on how I should proceed?

Thanks in advance,

Jooil

-- 
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Jooil Kim
Graduate Student
School of Earth and Environmental Sciences,
Seoul National University
Gwanak Gu Shillim 9 Dong San 56-1
Seoul National Univ. Bld#501, Rm 503
Seoul, Rep. of Korea 151-742
kji2080@gmail.com
tel) 82-2-877-6741
fax) 82-2-885-7164
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