Hi Tom,

What you said here works for numbers datatype but  my data type is factor
(levels). i am still very new to R. Please help.

library(sp)
data(meuse.grid)# "data.frame"
coordinates(meuse.grid) <- ~x+y
meuse.grid <- as(as(meuse.grid,
"SpatialPixelsDataFrame"),"SpatialGridDataFrame")#"SpatialGridDataFrame"
spplot(meuse.grid[,,"soil"])
meuse.grid$soil[meuse.grid$soil==1] <- NA
meuse.grid$soil[meuse.grid$soil==2 | meuse.grid$soil==3] <- 5
spplot(meuse.grid[,,"soil"])
summary(meuse.grid$soil)

Regards,

Nikki

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