| by.im {spatstat} | R Documentation |
Splits a pixel image into sub-images and applies a function to each sub-image.
## S3 method for class 'im': by(data, INDICES, FUN, ...)
data |
A pixel image (object of class "im"). |
INDICES |
Grouping variable.
Either a tessellation (object of class "tess") or
a factor-valued pixel image.
|
FUN |
Function to be applied to each sub-image of data. |
... |
Extra arguments passed to FUN. |
This is a method for the generic function by for
pixel images (class "im").
The pixel image data is first divided into sub-images according
to INDICES. Then the function FUN is applied to each subset.
The results of each computation are returned in a list.
The grouping variable INDICES may be either
"tess"). Each tile of
the tessellation delineates a subset of the spatial domain.
"im") with factor
values. The levels of the factor determine subsets of the spatial
domain.
A list containing the results of each evaluation of FUN.
Adrian Baddeley adrian@maths.uwa.edu.au http://www.maths.uwa.edu.au/~adrian/ and Rolf Turner r.turner@auckland.ac.nz
W <- square(1)
X <- as.im(function(x,y){sqrt(x^2+y^2)}, W)
Y <- dirichlet(runifpoint(12, W))
# mean pixel value in each subset
unlist(by(X, Y, mean))
# trimmed mean
unlist(by(X, Y, mean, trim=0.05))