Create a colour map for values of \(pH\).
pHcolourmap(range = c(0, 14), ..., n=256, step = FALSE)
pHcolour(pH)The return value of pHcolour is a character string or
a vector of character strings representing colours.
The return value of pHcolourmap
is a colour map (object of class "colourmap").
In chemistry the hydrogen potential \(pH\) measures how acidic or basic a solution is.
The function pHcolour calculates the colour associated with
a given value of \(pH\), according to a standard mapping in which
neutral \(pH=7\) is green,
acidic values \(pH < 7\) are yellow or red,
and basic values \(pH > 7\) are blue.
The function pHcolour takes a numerical value or vector of
values of \(pH\) and returns a character vector containing the
corresponding colours.
The function pHcolourmap produces a colour map for numerical values
of \(pH\), using the same consistent mapping of \(pH\)
values to colours.
The argument range specifies the range of \(pH\) values that
will be mapped by the resulting colour map. It should be a numeric
vector of length 2 giving the minimum and maximum values of \(pH\)
that the colour map will handle. (Colour maps created with different
values of range use essentially the same mapping of colours,
but when plotted as colour ribbons, display only the specified range.)
If step=FALSE (the default) the colours change
continuously with increasing values of the input. There will be
n different colour values in the colour map. Usually n
should be a large number.
If step=TRUE, the colour is constant on each unit interval of
\(pH\) values. That is, any value of \(pH\) in the interval
\([k, k+1]\), where \(k\) is an integer, will be mapped to the
same colour.
colourmap
pHcolour(7)
plot(pHcolourmap())
plot(pHcolourmap(step=TRUE))
plot(pHcolourmap(c(3, 8)))
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