Get Color on a Defined Color Range

Find a color on a defined color range depending on the value of x. This is helpful for colorcoding numeric values.

Usage

findCol(
  x,
  col = rev(heat.colors(100)),
  minX = NULL,
  maxX = NULL,
  all.inside = FALSE
)

Arguments

x: numeric.
col: a vector of colors.
minX: the x-value to be used for the left edge of the first color. If left to the default NULL min(pretty(x)) will be used.
maxX: the x-value to be used for the right edge of the last color. If left to the default NULL max(pretty(x)) will be used.
all.inside: logical; if true, the returned indices are coerced into 1, ..., N-1, i.e., 0 is mapped to 1 and N to N-1.

Value

A vector of the length of x with the colors assigned to the values, taken from col (names of col are kept). Values outside the range minX to maxX yield NA, unless all.inside is TRUE.

Details

For the selection of colors the option rightmost.closed in the used function findInterval() is set to TRUE. This will ensure that all values on the right edge of the range are assigned a color. How values outside the boundaries of minX and maxX should be handled can be controlled by all.inside. Set this value to TRUE, if those values should get the colors at the edges or set it to FALSE, if they should remain white (which is the default).

Note that findInterval() closes the intervals on the left side, e.g. [0, 1). This option can't be changed. Consequently will x-values lying on the edge of two colors get the color of the bigger one.

Examples



canvas(7, main="Use of function findCol()")

# get some data
x <- c(23, 56, 96)
# get a color range from blue via white to red
cols <- colorRampPalette(c("blue","white","red"))(100)
colLegend(x="bottomleft", col=cols, labels=seq(0, 100, 10), cex=0.8)

# and now the color coding of x:
(xcols <- findCol(x, cols, minX=0, maxX=100))
#> [1] "#7676FF" "#FFDDDD" "#FF0F0F"

# this should be the same as
cols[x+1]
#> [1] "#7676FF" "#FFDDDD" "#FF0F0F"

# how does it look like?
y0 <- c(-5, -2, 1)
text(x=1, y=max(y0)+2, labels="Color coding of x:")
text(x=1.5, y=y0, labels=x)
polygonX(regPolygon(x=3, y=y0, nVertices=4, startAngle=pi/4), col=xcols)
text(x=6, y=y0, labels=xcols)


# how does the function select colors?
canvas(xlim = c(0,1), ylim = c(0,1))
cols <- c(red="red", yellow="yellow", green="green", blue="blue")
colLegend(x=0, y=1, width=1, col=rev(cols), horiz = TRUE,
            labels=format(seq(0, 1, .25), digits=2, nsmall=2), 
            box=list(border="grey"), cex=0.8 )
x <- c(-0.2, 0, 0.15, 0.55, .75, 1, 1.3)
arrows(x0 = x, y0 = 0.6, y1 = 0.8, angle = 15, length = .2)
text(x=x, y = 0.5, labels = x, adj = c(0.5,0.5))
text(x=x, y = 0.4, labels = names(findCol(x, col=cols,
   minX = 0, maxX = 1, all.inside = TRUE)), adj = c(0.5,0.5))
text(x=x, y = 0.3, labels = names(findCol(x, col=cols,
   minX = 0, maxX = 1, all.inside = FALSE)), adj = c(0.5,0.5))