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Random sample

sampleRandom.Rd

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

Usage

# S4 method for class '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

Value

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)
#>  [1] 252.1049 356.3627 372.5424 412.5800 240.0186 704.8895 586.1123 298.1655
#>  [9] 221.0484 239.8339
 s <- stack(r, r)
 sampleRandom(s, size=5, cells=TRUE, sp=TRUE)
#>        coordinates cell   test.1   test.2
#> 1 (180420, 331540) 4931 205.5500 205.5500
#> 2 (179300, 330220) 7543 313.9919 313.9919
#> 3 (178900, 330300) 7373 423.6889 423.6889
#> 4 (179900, 331700) 4598 409.2047 409.2047
#> 5 (178940, 329820) 8334 402.6642 402.6642