Why cant i use vector in scale fill manual?

Question

I Want to create a graph that uses scale fill manual to fill colours of graph.

G3 <- ggplot(preTMM, aes(Var2, value, fill=group))+
  geom_boxplot()+
  Gtheme2+
  xlab("")+
  ylab("Log-CPM")+
  scale_fill_manual(values=c("pCDNA"="grey59","M"= "steelblue3"),
                    breaks=c("pCDNA","M"))+
  guides(fill=FALSE)

This works fine, but if i want to add it via a vector that was made previously;

DGEGroup1 <- "pCDNA"
DGEGroup2 <- "M" 
DGEGroup1Col <- "grey59"
DGEGroup2Col <- "steelblue3" 

it doesnt work.. what am I doing wrong.

G3 <- ggplot(preTMM, aes(Var2, value, fill=group))+
  geom_boxplot()+
  Gtheme2+
  xlab("")+
  ylab("Log-CPM")+
scale_fill_manual(values=c(DGEGroup1=DGEGroup1Col,DGEGroup2=DGEGroup1Col),
                    breaks=c(DGEGroup1,DGEGroup2))+
  guides(fill=FALSE)

I want to do this so all the graphs can be controlled by one colour vector if that makes sense?

Thanks in advance for help!

Answer 1

That syntax for a named vector doesn't work because R functions (including c()) don't require quotes for argument names:

x = "a"
y = "b"
c(x = y)
#   x 
# "b" 
## See how the name is literally `"x"`, not `"a"`

This is a Good Thing. It means that functions that have an argument named x don't break when you also have an object named x.

For your purpose, a good fix is to use setNames to name the vector. (You could also use names(vector) <- ... but setNames lets you keep it as a one-liner with an anonymous vector, much like you already have it).

values = setNames(
  c(DGEGroup1Col, DGEGroup2Col),
  nm = c(DGEGroup1, DGEGroup2)
)

However, if you're doing this for multiple plots I'd strongly suggest pulling out the definition of that vector earlier in you code so you're not repeating this syntax.