image-methods {Matrix}R Documentation

Methods for image() in Package 'Matrix'

Description

Methods for function image in package Matrix. An image of a matrix simply color codes all matrix entries and draws the n x m matrix using an n x m grid of (colored) rectangles.

Usage

## S4 method for signature 'dgTMatrix'
image(x,
      xlim = .5 + c(0, di[2]),
      ylim = .5 + c(di[1], 0), aspect = "iso",
      sub = sprintf("Dimensions: %d x %d", di[1], di[2]),
      xlab = "Column", ylab = "Row", cuts = 15,
      useRaster = FALSE,
      useAbs = NULL, colorkey = !useAbs,
      col.regions = NULL,
      lwd = NULL, ...)

Arguments

x

a Matrix object, i.e., fulfilling is(x, "Matrix").

xlim, ylim

x- and y-axis limits; may be used to “zoom into” matrix.

aspect

aspect ratio specified as number (y/x) or string; see levelplot.

sub, xlab, ylab

axis annotation with sensible defaults; see plot.default.

cuts

number of levels the range of matrix values would be divided into.

useRaster

logical indicating if raster graphics should be used (instead of the tradition rectangle vector drawing). If true, panel.levelplot.raster (from lattice package) is used, and the colorkey is also done via rasters, see also levelplot and possibly grid.raster.

Note that using raster graphics may often be faster, but can be slower, depending on the matrix dimensions and the graphics device (dimensions).

useAbs

logical indicating if abs(x) should be shown; if TRUE, the former (implicit) default, the default col.regions will be grey colors (and no colorkey drawn). The default is FALSE unless the matrix has no negative entries.

colorkey

logical indicating if a color key aka ‘legend’ should be produced. Default is to draw one, unless useAbs is true. You can also specify a list, see levelplot, such aslist(raster=TRUE) in the case of rastering.

col.regions

vector of gradually varying colors; see levelplot.

lwd

non-negative number or NULL (default), specifying the line-width of the rectangles of each non-zero matrix entry (drawn by grid.rect). The default depends on the matrix dimension and the device size.

...

further arguments passed to methods and levelplot, notably at for specifying (possibly non equidistant) cut values for dividing the matrix values (superseding cuts above).

Methods

All methods currently end up calling the method for the dgTMatrix class. Use showMethods(image) to list them all.

Examples

showMethods(image)
## If you want to see all the methods' implementations:
showMethods(image, incl=TRUE, inherit=FALSE)

data(CAex)
image(CAex, main = "image(CAex)")
image(CAex, useAbs=TRUE, main = "image(CAex, useAbs=TRUE)")

cCA <- Cholesky(crossprod(CAex), Imult = .01)
image(cCA, main="Cholesky(crossprod(CAex), Imult = .01)")
image(cCA, useAbs=TRUE)

data(USCounties)
image(USCounties)# huge
image(sign(USCounties))## just the pattern
    # how the result looks, may depend heavily on
    # the device, screen resolution, antialiasing etc
    # e.g. x11(type="Xlib") may show very differently than cairo-based

## Drawing borders around each rectangle;
    # again, viewing depends very much on the device:
image(USCounties[1:400,1:200], lwd=.1)
image(USCounties[1:200,1:200], lwd=.5)
image(USCounties[1:200,1:200], lwd=.01)

## Using raster graphics: For PDF this would give a 77 MB file,
## however, for such a large matrix, this is typically considerably
## *slower* (than vector graphics rectangles) in most cases :
if(doPNG <- !dev.interactive())
png("image-USCounties-raster.png", width=3200, height=3200)
image(USCounties, useRaster = TRUE) # should not suffer from anti-aliasing
if(doPNG)
   dev.off()
   ## and now look at the *.png image in a viewer you can easily zoom in and out
[Package Matrix version 1.0-6 Index]