Change order of one set of factors plotted in ggplot2

Question

I am creating a plot using ggplot2 which is almost perfect, it looks like this:

However, I want to change the order that the \'watering treatment\' boxes are sh

Answer 1

To get your colors in order, do the following: 1. Set the water column as a factor with the levels in the order that you want them to appear. 2. When setting the values in scale_fill_manual, set the colors in the order you want them to appear.

See below for result. Note that I removed your labels to make it more clear what colors correspond to what factor levels. You can add them back in, of course.

myDf = data.frame(
  Ring = c(1,1,1,1,1,2,2,2),
  CO2 = c(550,550,550,550,550,475,475,475),
  Water=c("B","P","R","W","Y","B","P","R"),
  "plot_NH4.2x25" = c(2.228750,4.945625,22.724375,-0.644375,-0.770000,2.228750,4.945625,1.348750)
)

myDf$Water = factor(myDf$Water, levels = c("R","Y","B","P","W"))


ggplot(data=myDf, aes(x=CO2, y=plot_NH4.2x25, fill=Water)) +
  stat_boxplot(geom ='errorbar', width = 0.5, position=position_dodge(0.75))+
  geom_boxplot()+
  theme_bw()+
  theme(panel.border = element_blank(),                            #remove box boarder
        axis.line.x = element_line(color="black", size = 0.5),      #add x axis line
        axis.line.y = element_line(color="black", size = 0.5),      #add y axis line
        panel.grid.major = element_blank(), panel.grid.minor = element_blank(),
        panel.grid.major = element_blank(), panel.grid.minor = element_blank(),
        legend.key.size = unit(1.5, 'lines'),
        legend.position=c(0.9,0.8),
        legend.key = element_blank(),    #remove grey box from around legend
        panel.grid.major = element_blank(), panel.grid.minor = element_blank())+
  scale_y_continuous(expand = c(0, 0), limits = c(-5,140), breaks=seq(0,140,20))+     #change x axis to intercept y axis at 0
  scale_fill_manual(values=c("firebrick1", "yellow2","skyblue2", "orchid1",  "seagreen3"),
                    name=" Watering treatment")+
  ylab(expression(Membrane~available~NH[4]^{" +"}~-N~(~mu~g~resin^{-1}~14~day^{-1})))+
  xlab(expression(CO[2]~concentration~(mu~mol~mol^{-1})))

Note that my plot below doesn't match yours (presumably) due to the limited number of rows provided.