How to reorder fill factor within the x-axis?

Question

I would like to reorder the groupings on the x-axis in a particular way, so that the order of my "Sites" at each "Month" is BTH, FOX, MEF, DUR. As of right now, the Sites are ordered alphabetically.

Site Month N flux N flux_SE
BTH May 0.047 0.009
BTH Jun 0.974 0.14
BTH Jul 0.698 0.124
BTH Aug 0.112 0.017
BTH Sep 0.107 0.019
BTH Oct 0.234 0.018
FOX May 0.072 0.02
FOX Jun 0.562 0.094
FOX Jul 0.250 0.056
FOX Aug 0.097 0.017
FOX Sep 0.105 0.015
FOX Oct 0.409 0.078
MEF May 0.072 0.025
MEF Jun 0.434 0.167
MEF Jul 0.224 0.058
MEF Aug 0.132 0.047
MEF Sep 0.073 0.024
MEF Oct 0.271 0.08
DUR May 0.039 0.01
DUR Jun 0.342 0.155
DUR Jul 0.175 0.044
DUR Aug 0.065 0.018
DUR Sep 0.061 0.021
DUR Oct 0.279 0.067


flux$Month = factor(N_flux$Month, levels = month.abb)  #This will get the motnhs in chronological order using 3-letter month abbreviations

ggplot(N_flux, aes(x=Month, y=N.flux, fill=factor(Site), reorder(month,month.name))) + #this code makes a 4-panel bar graph by site
  geom_bar(stat="identity", colour="black",position=position_dodge(.9)) +
  scale_y_continuous(expand = c(0,0), limits = c(0,1.5), breaks = seq(0,1.5, by=.2)) +    
  ylab(expression("Nitrogen flux (g N m"*{}^-2*")")) + xlab("Month") + labs(fill = "Site") +
  theme_bw() +
  theme(panel.border = element_rect(color = "black", fill = NA),
        strip.text.x = element_text(colour = 'black', size = 15, face = "bold"),
        axis.text = element_text(colour = "black"),
        panel.grid.major = element_blank(), panel.grid.minor = element_blank(),
        legend.position = c(0.9,0.82), legend.text = element_text(size = 9),
        legend.key.size = unit(.55, "cm")) +
  scale_fill_manual(values = c("black", "grey70","grey50", "white")) +
  geom_errorbar(aes(ymin=N.flux, ymax=N.flux+N.flux_SE), size=0.5,                          
                width=.25,position=position_dodge(.9))

Figure I have so far...

Answer 1

You just need to set the column as a factor, much like you did for Month, and specify the levels. Add this line.

N_flux$Site = factor(N_flux$Site, levels = c("BTH", "FOX", "MEF", "DUR"))

Then, you can change the first line of your ggplot command.

ggplot(N_flux, aes(x=Month, y=N.flux, fill=Site, reorder(month,month.name))) +

Since it's already a factor, no need to create a factor again.