colourmap
Colour Lookup Tables
Create a colour map (colour lookup table).
Usage
colourmap(col, ..., range=NULL, breaks=NULL, inputs=NULL)
Arguments
- col
- Vector of values specifying colours
- ...
- Ignored.
- range
- Interval to be mapped.
A numeric vector of length 2, specifying the endpoints of the
range of values to be mapped.
Incompatible with
breaks
orinputs
. - inputs
- Values to which the colours are associated.
A factor or vector of the same length as
col
. Incompatible withbreaks
orrange
. - breaks
- Breakpoints for the colour map.
A numeric vector of length equal to
length(col)+1
. Incompatible withrange
orinputs
.
Details
A colour map is a mechanism for associating colours with data. It can be regarded as a function, mapping data to colours.
The command colourmap
creates an object representing
a colour map, which can then be used to control the plot commands
in the
The argument col
specifies the colours to which
data values will be mapped. It should be a vector
whose entries can be interpreted as colours by the standard
Rgraphics system. The entries can be string names of colours
like "red"
, or integers that refer to
colours in the standard palette, or strings containing
six-letter hexadecimal codes like "#F0A0FF"
.
Exactly one of the arguments range
, inputs
or breaks
must be specified by name.
If inputs
is given, then it should be a vector or factor,
of the same length as col
. The entries of inputs
can be
any atomic type (e.g. numeric, logical, character, complex) or factor
values. The resulting colour map associates the value inputs[i]
with the colour col[i]
.
If range
is given, then it determines the interval of the real
number line that will be mapped. It should be a numeric vector of
length 2.
If breaks
is given, then it determines the precise intervals
of the real number line
which are mapped to each colour. It should be a numeric vector,
of length at least 2, with entries that are in increasing order.
Infinite values are allowed. Any number in the range
between breaks[i]
and breaks[i+1]
will be mapped to the
colour col[i]
.
The result is an object of class "colourmap"
.
There are print
and plot
methods for this class.
Some plot commands in the
The result is also a function f
which can be used to compute
the colour assigned to any data value.
That is, f(x)
returns the character value of the colour assigned
to x
. This also works for vectors of data values.
Value
- A function, which is also an object of class
"colourmap"
.
See Also
The plot method plot.colourmap
.
See the Rhelp file on
colours
for information about the colours
that Rrecognises, and how to manipulate them.
To make a smooth transition between colours, see
interp.colourmap
.
To alter individual colour values, see
tweak.colourmap
.
See colourtools
for more tools to manipulate colour values.
See lut
for lookup tables.
Examples
# colour map for real numbers, using breakpoints
cr <- colourmap(c("red", "blue", "green"), breaks=c(0,5,10,15))
cr
cr(3.2)
cr(c(3,5,7))
# a large colour map
co <- colourmap(rainbow(100), range=c(-1,1))
co(0.2)
# colour map for discrete set of values
ct <- colourmap(c("red", "green"), inputs=c(FALSE, TRUE))
ct(TRUE)