Question

The ggplot2 manual at http://had.co.nz/ggplot2/scale_manual.html suggests using a structure like:

values = c("8" = "red","4" = "blue","6" = "darkgreen", "10" = "orange")

to assign specific colours to values.

How does one generate this structure from two arrays:

A = c("8","4","6","10"); B = c("red","blue","darkgreen","orange")

I got as far as:

rbind(A,B)
  [,1]  [,2]   [,3]        [,4]    
A "8"   "4"    "6"         "10"    
B "red" "blue" "darkgreen" "orange"

But I am not sure how to turn that into an array of “X” = “Y” assignments.

I realise this is a general R question, not one specific to ggplot2. But I’m tagging it ggplot2 in case it helps someone with the same issue in the future. Any advice welcomed…

Answer 1

This should work:

values = B
names(values) = A
> all.equal(values,
+       c("8" = "red","4" = "blue","6" = "darkgreen", "10" = "orange"))
[1] TRUE

The behavior you are after mimics that of a Python dictionary. There are key,value pairs, and referring to a specific key returns the value. In this R example the keys are the names of the character vector, and the values are the values inside the vector. For ggplot2 this explicitly couples a key (e.g. "8") to a color value ("red").