terra: app – R documentation

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app

Apply a function to the cells of a SpatRaster

Description

Apply a function to values of each cell of a SpatRaster. Similar to apply – think of each layer in a SpatRaster as a column (or row) in a matrix. This is generally used to summarize the values of multiple layers into one layer; but this is not required.

You can also apply a function fun across datasets by layer of a SpatRasterDataset. In that case, summarization is across SpatRasters, not across layers.

Usage

## S4 method for signature 'SpatRaster'
app(x, fun, ..., cores=1, filename="", overwrite=FALSE, wopt=list())

## S4 method for signature 'SpatRasterDataset'
app(x, fun, ..., cores=1, filename="", overwrite=FALSE, wopt=list())

Arguments

`x`	SpatRaster or SpatRasterDataset
`fun`	function
`...`	additional arguments for `fun`
`cores`	positive integer. If `cores > 1`, a 'parallel' package cluster with that many cores is created and used. Ignored for C++ level implemented functions "max", "min", "mean", "range", "prod", "sum", "any", and "all"
`filename`	character. Output filename
`overwrite`	logical. If `TRUE`, `filename` is overwritten
`wopt`	list with named options for writing files as in `writeRaster`

Details

To speed things up, parallelization is supported, but this is often not helpful, and it may actually be slower. There is only a speed gain if you have many cores (> 8) and/or a very complex (slow) function fun. If you write fun yourself, consider supplying a cppFunction made with the Rcpp package instead (or go have a cup of tea while the computer works for you).

Value

SpatRaster

Examples

r <- rast(ncols=10, nrows=10)
values(r) <- 1:ncell(r)
x <- c(r, sqrt(r), r-50)
s <- app(x, fun=sum)
s
# for a few generic functions like 
# "sum", "mean", and "max" you can also do
sum(x)

## SpatRasterDataset
sd <- sds(x, x*2, x/3)
a <- app(sd, max)
a
# same as 
max(x, x*2, x/3)

## also works for a single layer
f <- function(i) (i+1) * 2 * i + sqrt(i)
s <- app(r, f)
# same as above, but that is not memory-safe
# and has no filename argument 
s <- f(r)

terra

Spatial Data Analysis

v1.2-10

GPL (>= 3)

Authors

Robert J. Hijmans [cre, aut] (<https://orcid.org/0000-0001-5872-2872>), Roger Bivand [ctb] (<https://orcid.org/0000-0003-2392-6140>), Karl Forner [ctb], Jeroen Ooms [ctb] (<https://orcid.org/0000-0002-4035-0289>), Edzer Pebesma [ctb] (<https://orcid.org/0000-0001-8049-7069>)

Initial release

2021-05-12

app