ggplot pie charts / bar graph, force a legend [duplicate] - r

Question

I'm struggling with ggplot (I always do). There are a number of very similar questions about forcing ggplot to include zero value categories in legends - here and here (for example). BUT I (think I) have a slightly different requirement to which all my mucking about with scale_x_discrete and scale_fill_manual has not helped.
Requirement: As you can see; the right-hand plot has no data in the TM=5 category - so is missing. What I need is for that right plot to have category 5 shown on the axis but obviously with no points or box.
Current Plot Script:
#data
plotData <- data.frame("TM" = c(3,2,3,3,3,4,3,2,3,3,4,3,4,3,2,3,2,2,3,2,3,3,3,2,3,1,3,2,2,4,4,3,2,3,4,2,3),
"Score" = c(5,4,4,4,3,5,5,5,5,5,5,3,5,5,4,4,5,4,5,4,5,4,5,4,4,4,4,4,5,4,4,5,3,5,5,5,5))
#vars
xTitle <- bquote("T"["M"])
v.I <- plotData$TM
depVar <- plotData$Score
#plot
p <- ggplot(plotData, aes_string(x=v.I,y=depVar,color=v.I)) +
geom_point() +
geom_jitter(alpha=0.8, position = position_jitter(width = 0.2, height = 0.2)) +
geom_boxplot(width=0.75,alpha=0.5,aes_string(group=v.I)) +
theme_bw() +
labs(x=xTitle) +
labs(y=NULL) +
theme(legend.position='none',
axis.text=element_text(size=10, face="bold"),
axis.title=element_text(size=16))
Attempted Solutions:
drop=False to scales (suggested by #Jarretinha here) totally borks margins and x-axis labels
> plot + scale_x_discrete(drop=FALSE) + scale_fill_manual(drop=FALSE)
Following logic from here and manually setting the labels in scale_fill_manual does nothing and results in the same right-hand plot from example above.
> p + scale_fill_manual(values = c("red", "blue", "green", "purple", "pink"),
labels = c("Cat1", "Cat2", "Cat3", "Cat4", "Cat5"),
drop=FALSE)
Playing with this logic and trying something with scale_x_discrete results in a change to category names on x-axis but the fifth is still missing AND the margins (as attempt 1) are borked again. BUT apparent that scale_x_discrete is important and NOT the whole answer
> p + scale_x_discrete(limits = c("Cat1", "Cat2", "Cat3", "Cat4", "Cat5"), drop=FALSE)
ANSWER for above example courtesy of input from #Bouncyball & #aosmith
#data
plotData <- data.frame("TM" = c(3,2,3,3,3,4,3,2,3,3,4,3,4,3,2,3,2,2,3,2,3,3,3,2,3,1,3,2,2,4,4,3,2,3,4,2,3),
"Score" = c(5,4,4,4,3,5,5,5,5,5,5,3,5,5,4,4,5,4,5,4,5,4,5,4,4,4,4,4,5,4,4,5,3,5,5,5,5))
plotData$TM <- factor(plotData$TM, levels=1:5) # add correct (desired number of factors to input data)
#vars
xTitle <- bquote("T"["M"])
v.I <- plotData$TM
depVar <- plotData$Score
myPalette <- c('#5c9bd4','#a5a5a4','#4770b6','#275f92','#646464','#002060')
#plot
ggplot(plotData, aes_string(x=v.I,y=depVar,color=v.I)) +
geom_jitter(alpha=0.8, position = position_jitter(width = 0.2, height = 0.2)) +
geom_boxplot(width=0.75,alpha=0.5,aes_string(group=v.I)) +
scale_colour_manual(values = myPalette, drop=F) + # new line added here
scale_x_discrete(drop=F) + # new line added here
theme_bw() +
labs(x=xTitle) +
labs(y=NULL) +
theme(legend.position='none',
axis.text=element_text(size=10, face="bold"),
axis.title=element_text(size=16))

Answer 1

Here's a workaround you could use:
# generate dummy data
set.seed(123)
df1 <- data.frame(lets = sample(letters[1:4], 20, replace = T),
y = rnorm(20), stringsAsFactors = FALSE)
# define factor, including the missing category as a level
df1$lets <- factor(df1$lets, levels = letters[1:5])
# make plot
ggplot(df1, aes(x = lets, y = y))+
geom_boxplot(aes(fill = lets))+
geom_point(data = NULL, aes(x = 'e', y = 0), pch = NA)+
scale_fill_brewer(drop = F, palette = 'Set1')+
theme_bw()
Basically, we plot an "empty" point (i.e. pch = NA) so that the category shows up on the x-axis, but has no visible geom associated with it. We also define our discrete variable, lets as a factor with five levels when only four are present in the data.frame. The missing category is the letter e.
NB: You'll have to adjust the positioning of this "empty" point so that it doesn't skew your y axis.
Otherwise, you could use the result from this answer to avoid having to plot an "empty" point.
# generate dummy data
set.seed(123)
df1 <- data.frame(lets = sample(letters[1:4], 20, replace = T),
y = rnorm(20), stringsAsFactors = FALSE)
# define factor, including the missing category as a level
df1$lets <- factor(df1$lets, levels = letters[1:5])
# make plot
ggplot(df1, aes(x = lets, y = y)) +
geom_boxplot(aes(fill = lets)) +
scale_x_discrete(drop = F) +
scale_fill_brewer(drop = F, palette = 'Set1') +
theme_bw()