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

findColor(
  x,
  col = rev(heat.colors(100)),
  minX = NULL,
  maxX = NULL,
  allInside = 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.

allInside

logical; if true, the returned indices are coerced into 1, ..., N-1, i.e., 0 is mapped to 1 and N to N-1.

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 allInside. 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.

See also

findInterval()

Other color.lookup: contrastColor()

Examples

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

# 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 <- findColor(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)
polygon(regPolygon(x=3, y=y0, numVertices=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), 
            frame="grey", cex=0.8 )
#> Warning: "frame" is not a graphical parameter
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(findColor(x, col=cols,
   minX = 0, maxX = 1, allInside = TRUE)), adj = c(0.5,0.5))
text(x=x, y = 0.3, labels = names(findColor(x, col=cols,
   minX = 0, maxX = 1, allInside = FALSE)), adj = c(0.5,0.5))