Calculate values such as a correlation coefficient for focal regions in two neighboring layers. A function is applied to the first and second layer, then to the second and third layer, etc.

## Usage

``````# S4 method for class 'SpatRaster'
focalPairs(x, w=3, fun, ..., fillvalue=NA,
filename="", overwrite=FALSE, wopt=list())``````

## Arguments

x

SpatRaster with at least two layers

w

numeric or matrix to define the focal window. The window an be defined as one (for a square) or two numbers (row, col); or with an odd-sized weights matrix. See the Details section in `focal`. Note that if a matrix with numbers other than zero or one are used, the values are used as weights. For this to work, `fun` must have an argument `weights`

fun

a function with at least two arguments (one for each layer). There is a built-in function "pearson" (for both the weighted and the unweighted Pearson correlation coefficient. This function has an additional argument `na.rm=FALSE`

...

additional arguments for `fun`

fillvalue

numeric. The value of the cells in the virtual rows and columns outside of the raster

filename

character. Output filename

overwrite

logical. If `TRUE`, `filename` is overwritten

wopt

additional arguments for writing files as in `writeRaster`

## Value

SpatRaster

`layerCor`, `focalReg`, `focal`, `focal3D`

## Examples

``````r <- rast(system.file("ex/logo.tif", package="terra"))
set.seed(0)
r[[1]] <- flip(r[[1]], "horizontal")
r[[2]] <- flip(r[[2]], "vertical") + init(rast(r,1), runif)
r[[3]] <- init(rast(r,1), runif)

x <- focalPairs(r, w=5, "pearson", na.rm=TRUE)
plot(x)

# suppress warning "the standard deviation is zero"
suppressWarnings(x <- focalPairs(r, w=5, "pearson", use="complete.obs"))

z <- focalPairs(r, w=9, function(x, y) mean(x) + mean(y))
``````