raster (version 1.7-23)

zonal: Zonal statistics

Description

Compute zonal statistics. That is, cross-tabulate the values of a Raster* object based on a "zones" RasterLayer. NA values are removed.

Usage

zonal(x, zones, stat='mean', digits=0, progress)

Arguments

x

Raster* object

zones

RasterLayer object with codes representing zones

stat

The function to be applied. Either as character: 'mean', 'min', 'max', 'sum'; or a function (see Details)

digits

Integer. Number of digits to maintain in 'zones'. By default averaged to an integer (zero digits)

progress

Character. "text", "window", or "" (the default, no progress bar)

Value

• A matrix with a value for each zone (unique value in zones)

Details

If stat is a function, zonal will fail (gracefully) for very large RasterLayers

Examples

r <- raster(ncols=10, nrows=10)
r[] <- runif(ncell(r)) * 1:ncell(r)
z <- r
z[] <- rep(1:5, each=20)
zonal(r, z, mean)
zonal(r, z, min)
# for big files, use a character value rather than a function
zonal(r, z, 'sum')

# multiple layers
zonal(stack(r, r*10), z, 'sum')