Colour a line by a given value in a plot in R

Question

Advancing on the answer given here where the same question was asked for a scatter plot, is it possible to plot a line where the colour is based on the y value?

Example data

x = 1:11
y = abs(6 - x)
plot(1:22,c(y,y), col = ifelse(c(y,y) < 2.5, 2, 3), pch = 16)

Will give

However, trying

plot(1:22,c(y,y), col = ifelse(c(y,y) < 2.5, 2, 3), type = "l")

Gives

or doing lines on y<2.5 which gives

instead of the solution I am after, which is

Is there any easy method to do this? This is only a simple case, and I can't manually add each section to my actual data. Thanks!

Answer 1

Try this

x = 1:11
y = abs(6 - x)
y = c(y,y)
plot(1:22,y, col = ifelse(c(y,y) < 2.5, 2, 3), pch = 16)



for(i in 1:21){
  if(y[i]>1.9&& y[i+1]>1.9){
    linecolour="green"
  } else {
    linecolour="red"
  }
  lines(c((1:22)[i],(1:22)[i+1]),c(y[i],y[i+1]),col=linecolour)
}