geom_dotplot() loses dodge after applying colour aesthetics

Question

I want to organize my data by one category on the X-axis, but color it by another category as in this example:

Graph 1, without coloring:

require(ggplot2)
nocolor <- ggplot(mtcars, aes(x=as.factor(cyl), y=disp)) + 
  geom_dotplot(binaxis="y", stackdir = "center")
print(nocolor)

Graph 2, with coloring:

nododge <- ggplot(mtcars, aes(x=as.factor(cyl), y=disp, fill=as.factor(gear))) + 
  geom_dotplot(binaxis="y", stackdir = "center")
print(nododge)

One problem that occurs after introducing coloring is that the dots belonging to different groups wont dodge one another anymore. This causes problems with my real data, as I get dots that happen to have the same value and completely obscure one another.

Then I tried this, but it garbled my data:

Graph 3:

garbled <- ggplot(mtcars, aes(x=as.factor(cyl), y=disp)) +
  geom_dotplot(binaxis="y", stackdir = "center", fill=as.factor(mtcars$gear))
print(garbled)

The dots dodge one another, but the the coloring is just random and is not true to the actual data.

I expected the answer to this question to solve my problem, but the coloring remained random:

Graph 4:

graphdata <- mtcars
graphdata$colorname <- as.factor(graphdata$gear) 
levels(graphdata$colorname) <- c("red", "blue", "black")
jalapic <- ggplot(graphdata, aes(x=as.factor(cyl), y=disp)) +
  geom_dotplot(binaxis="y", stackdir = "center", fill=as.character(graphdata$colorname))
print(jalapic)

Does anyone have an idea how to get the dots in Graph #2 to dodge one another, or how to fix the coloring in graphs 3 or 4? I would really appreciate any help, thanks.

Answer 1

Using binpositions = "all" and stackgroups = TRUE:

ggplot(mtcars, aes(x=as.factor(cyl), y=disp, fill=as.factor(gear))) + 
  geom_dotplot(binaxis="y", stackdir = "center", binpositions="all", stackgroups=TRUE)

gives:

A possible alternative is using stackdir = "up":

ggplot(mtcars, aes(x=as.factor(cyl), y=disp, fill=as.factor(gear))) + 
  geom_dotplot(binaxis="y", stackdir = "up", binpositions="all", stackgroups=TRUE)

which gives: