CODEWITHSUNDEEP
r
Beavis
Beavis

Reputation: 498

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

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 scatter

However, trying 

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

Gives

bad

or doing lines on y<2.5 which gives

enter image description here

instead of the solution I am after, which is

enter image description here

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!

Upvotes: 4

Views: 999

Answers (2)

Rui Barradas
Rui Barradas

Reputation: 76683

Here is a vectorized solution. It is partly based on the answers to this question with the main difference that the function plotted there is a smooth function, unlike this one. This makes a difference when computing the points to plot and their colors. 

fun <- function(x) abs(6 - x)

x <- 1:11
y <- fun(x)
X <- c(x, x + 11)
Y <- c(y, y)
n <- length(X)

color <- ifelse((Y[-n] < 2.5) & (Y[-1] < 2.5), 2, 3)

plot(X, Y, col = color, pch = 16)
segments(x0 = X[-n], y0 = Y[-n], 
         x1 = X[-1], y1 = Y[-1],
         col = color, pch = 16)

enter image description here

To remove the points, start with

plot(X, Y, type = "n")

Upvotes: 0

Daniel O
Daniel O

Reputation: 4358

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)
}

enter image description here

Upvotes: 4

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