rasterToPolygons(raster, fun=NULL)
fun
should be a simple function returning a logical value
e.g.: fun=function(x){x==1}
or fun=function(x){x>3}
r <- raster(nrow=18, ncol=36)
r[] <- runif(ncell(r)) * 10
r[r>8] <- NA
pol <- rasterToPolygons(r, fun=function(x){x>6})
#plot(r)
#plot(pol, add=T, col='red')
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