have plot points coloured on a spectrum in R

Question

I have a list of points that I want to play on a graph in R. In a bid to have 3 levels of information (X axis, Y axis and another) I want to plot the points on a graph and colour them on a scale for the 3rd variable. I have a percentage value for each point that I want displayed as the third variable (Z). So if A has a Z value of 0.95, I want it a bright red, but as B only has Z = 0.65, I want it dull red heading to blue. Values go from NA (which should be blue I suppose) to 0.99 (bright red). Sample data: ``` 1 1 0.02937715 2 1 0.05872889 3 1 0.08802983 4 1 0.11725462 5 1 0.14637799 6 1 0.17537475 7 1 0.20421981 8 1 0.23288821 9 1 0.26135518 10 1 0.28959607 ``` The third column gives the Z values.

Accepted Answer

Some reproducible data to play with would be helpful:

```
DF <- expand.grid(x=1:100, y=1:100)
DF$z <- abs(sin(DF$x/34) * cos(DF$y/22))
```

`x` and `y` are a grid from 1 to 100; `z` ranges between 0 and 1 (the function is nothing in particular, just something that stays between 0 and 1 and doesn't have extremely simple structure).

Base graphics

```
plot(DF$x, DF$y, col=rgb((colorRamp(c("blue", "red"))(DF$z))/255), pch=19)
```

ggplot2

```
library("ggplot2")
ggplot(DF, aes(x, y, colour=z)) +
  geom_point(shape=19) +
  scale_colour_gradient(low="blue", high="red")
```

have plot points coloured on a spectrum in R

Solution

Problem