sampleRandom: Random sample

In raster: Geographic Data Analysis and Modeling

Description

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

Usage

## 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

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)
 s <- stack(r, r)
 sampleRandom(s, size=5, cells=TRUE, sp=TRUE)

Example output

Loading required package: sp
 [1] 757.740 969.852 768.547 282.222 483.113 428.305 380.700 293.529 464.482
[10] 422.541
class       : SpatialPointsDataFrame 
features    : 5 
extent      : 178860, 181180, 330300, 333700  (xmin, xmax, ymin, ymax)
coord. ref. : +init=epsg:28992 +towgs84=565.237,50.0087,465.658,-0.406857,0.350733,-1.87035,4.0812 +proj=sterea +lat_0=52.15616055555555 +lon_0=5.38763888888889 +k=0.9999079 +x_0=155000 +y_0=463000 +ellps=bessel +units=m +no_defs 
variables   : 3
names       : cell,           test.1,           test.2 
min values  :  630, 313.378997802734, 313.378997802734 
max values  : 7372, 810.278991699219, 810.278991699219 

raster documentation built on Jan. 5, 2021, 3:01 a.m.