by.im

0th

Percentile

Apply Function to Image Broken Down by Factor

Splits a pixel image into sub-images and applies a function to each sub-image.

Keywords
manip, methods, spatial
Usage
## S3 method for class 'im':
by(data, INDICES, FUN, ...)
Arguments
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.
Details

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.

Value

  • A list containing the results of each evaluation of FUN.

See Also

split.im, tess, im

Aliases
  • by.im
Examples
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))
Documentation reproduced from package spatstat, version 1.27-0, License: GPL (>= 2)

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