Apply Function to Image Broken Down by Factor
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 |
INDICES |
Grouping variable.
Either a tessellation (object of class |
FUN |
Function to be applied to each sub-image of |
... |
Extra arguments passed to |
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
a tessellation (object of class "tess"). Each tile of
the tessellation delineates a subset of the spatial domain.
a pixel image (object of class "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.Baddeley@curtin.edu.au
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(runifrect(12, W))
# mean pixel value in each subset
unlist(by(X, Y, mean))
# trimmed mean
unlist(by(X, Y, mean, trim=0.05))Please choose more modern alternatives, such as Google Chrome or Mozilla Firefox.