r <- raster(ncols=36, nrows=18)
n <- 1000
x <- runif(n)* 360 - 180
y <- runif(n)* 180 - 90
xy <- cbind(x, y)
vals <- rep(1, n)
r <- pointsToRaster(r, xy, vals)
# now with an sp SpatialPointsDataFrame object
p <- as.data.frame(cbind(xy, vals))
coordinates(p) <- ~x+y
r <- pointsToRaster(r, p, p@data[,'vals'])
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