sampleRandom function

Random sample

Take a random sample from the cell values of a Raster* object (without replacement).

## S4 method for signature 'Raster'
sampleRandom(x, size, na.rm=TRUE, ext=NULL, 
    cells=FALSE, rowcol=FALSE, xy=FALSE, sp=FALSE, asRaster=FALSE, ...)

Arguments

• x: Raster* object
• size: positive integer giving the number of items to choose
• na.rm: logical. If TRUE (the default), NA values are removed from random sample
• ext: Extent object. To limit regular sampling to the area within the extent
• cells: logical. If TRUE, sampled cell numbers are also returned
• rowcol: logical. If TRUE, sampled row and column numbers are also returned
• xy: logical. If TRUE, coordinates of sampled cells are also returned
• sp: logical. If TRUE, a SpatialPointsDataFrame is returned
• asRaster: logical. If TRUE, a Raster* object is returned with random cells with values, all other cells with NA
• ...: Additional arguments as in writeRaster. Only relevant when asRaster=TRUE

Details

With argument na.rm=TRUE, the returned sample may be smaller than requested

Returns

A vector, matrix (if cells=TRUE or x is a multi-layered object), or a SpatialPointsDataFrame (if sp=TRUE )

See Also

sampleRegular, sampleStratified

Examples

r <- raster(system.file("external/test.grd", package="raster"))
 sampleRandom(r, size=10)
 s <- stack(r, r)
 sampleRandom(s, size=5, cells=TRUE, sp=TRUE)