How to block a part of the level plot in R made using lattice package?

I have made a level plot in R of a variable using the lattice package. This grid corresponds to South Asia. I am only interested in viewing the values of this variable (aerosol optical depth) for certain countries in South Asia. I have a dummy variable that takes the value 1 for the countries I am interested开发者_运维技巧 in and 0 otherwise. Is it possible for me to colour this part of the grid black or any other colour?

I cannot show the level plot as I am low on reputation with stackoverflow. (The pdf that was attached to the crossposted message to rhelp should now appear:)

Here is my R code:

levelplot(aod ~ longitude + latitude | factor(day), data = aod_Jan, 
    aspect="iso", contour = TRUE, layout=c(1,1))

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Since you are using geographical data, maybe the raster package is useful for you. For example, let's display the altitude of France (download this zip file or use the raster::getData function). After you unzip the file:

library(raster)
fraAlt <- raster('FRA_alt')
plot(fraAlt) ## Not only France is displayed...

If you want to display only the altitude of France, you need the information of the boundaries: download this RData file (or use the raster::getData function). This RData contains a SpatialPolygonsDataFrame (named gadm) which can be converted to a Raster with:

 mk <- rasterize(gadm, fraAlt)

Now you can mask the altitude raster with the boundaries:

 fraAltMask <- mask(fraAlt, x)
 plot(fraAltMask) ##Now only France is displayed

Finally, if you want to use lattice methods you need the rasterVis package:

 library(rasterVis)
 levelplot(fraAlt)
 levelplot(fraAltMask)

Now, all together with the boundaries superimposed:

 s <- stack(fraAlt, fraAltMask)
 layerNames(s) <- c('Alt', 'AltMask')
 boundaries <- as(gadm, 'SpatialLines')
 levelplot(s) + layer(sp.lines(boundaries))

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Use the subset argument to levelplot. Perhaps:

levelplot(aod ~ longitude + latitude | factor(day), data = aod_Jan, subset = dummy==1,
    aspect="iso", contour = TRUE, layout=c(1,1))