R: High-performance rectangular tiling.

geom_raster {ggplot2}

R Documentation

High-performance rectangular tiling.

Description

This is a special case of geom_tile where all tiles are the same size. It is implemented highly efficiently using the internal rasterGrob function.

Usage

geom_raster(mapping = NULL, data = NULL, stat = "identity",
  position = "identity", hjust = 0.5, vjust = 0.5, interpolate = FALSE,
  ...)

Arguments

`mapping`	The aesthetic mapping, usually constructed with `aes` or `aes_string`. Only needs to be set at the layer level if you are overriding the plot defaults.
`data`	A layer specific dataset - only needed if you want to override the plot defaults.
`stat`	The statistical transformation to use on the data for this layer.
`position`	The position adjustment to use for overlapping points on this layer
`hjust,vjust`	horizontal and vertical justification of the grob. Each justification value should be a number between 0 and 1. Defaults to 0.5 for both, centering each pixel over its data location.
`interpolate`	If `TRUE` interpolate linearly, if `FALSE` (the default) don't interpolate.
`...`	other arguments passed on to `layer`. This can include aesthetics whose values you want to set, not map. See `layer` for more details.

Details

By default, geom_raster add a vertical and horizontal padding. The size of padding depends on the resolution of data. If you want to manually set the padding (e.g. want zero-padding), you can change the behavior by setting hpad and vpad.

Aesthetics

geom_raster understands the following aesthetics (required aesthetics are in bold):

x
y
alpha
fill

Examples


# Generate data
pp <- function (n,r=4) {
 x <- seq(-r*pi, r*pi, len=n)
 df <- expand.grid(x=x, y=x)
 df$r <- sqrt(df$x^2 + df$y^2)
 df$z <- cos(df$r^2)*exp(-df$r/6)
 df
}
qplot(x, y, data = pp(20), fill = z, geom = "raster")
# Interpolation worsens the apperance of this plot, but can help when
# rendering images.
qplot(x, y, data = pp(20), fill = z, geom = "raster", interpolate = TRUE)

# For the special cases where it is applicable, geom_raster is much
# faster than geom_tile:
pp200 <- pp(200)
base <- ggplot(pp200, aes(x, y, fill = z))
benchplot(base + geom_raster())
benchplot(base + geom_tile())

# justification
df <- expand.grid(x = 0:5, y = 0:5)
df$z <- runif(nrow(df))
# default is compatible with geom_tile()
ggplot(df, aes(x, y, fill = z)) + geom_raster()
# zero padding
ggplot(df, aes(x, y, fill = z)) + geom_raster(hjust = 0, vjust = 0)

[Package ggplot2 version 1.0.1 Index]