Question

My colleague and I are trying to order a stacked bar graph based on the y-values instead of alphabetically by the x-values.

The sample data is:

library(ggplot2)
samp.data <- structure(list(fullname = c("LJ", "PR", 
                                         "JB", "AA", "NS", 
                                         "MJ", "FT", "DA", "DR", 
                                         "AB", "BA", "RJ", "BA2", 
                                         "AR", "GG", "RA", "DK", 
                                         "DA2", "BJ2", "BK", "HN", 
                                         "WA2", "AE2", "JJ2"), I = c(2L, 
                                                                     1L, 3L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 3L, 2L, 3L, 3L, 3L, 
                                                                     3L, 3L, 3L, 3L, 3L, 3L, 3L), S = c(1L, 1L, 1L, 1L, 2L, 2L, 2L, 
                                                                                                        2L, 2L, 2L, 2L, 3L, 2L, 3L, 2L, 2L, 2L, 3L, 2L, 3L, 2L, 3L, 3L, 
                                                                                                        3L), D = c(2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 
                                                                                                                   2L, 2L, 3L, 3L, 2L, 3L, 3L, 3L, 2L, 3L, 3L), C = c(0L, 2L, 1L, 
                                                                                                                                                                      2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 3L, 
                                                                                                                                                                      2L, 3L, 3L, 3L, 3L)), .Names = c("fullname", "I", "S", "D", "C"
                                                                                                                                                                      ), class = "data.frame", row.names = c(NA, 24L))
md <- reshape2::melt(samp.data, id = (c("fullname")))
ggplot(data = md, aes(x = fullname, y = value, fill = variable)) +
  geom_col()

But I ultimately want to sort by the sum of the 4 variables (I, S, D, and C) instead of the alphabetical order of the fullnames.

Answer 1

The general (non ggplot-specific) answer is to use reorder() to reset the factor levels in a categorical column, based on some function of the other columns.

## Examine the default factor order
levels(samp.data$fullname)

## Reorder fullname based on the the sum of the other columns
samp.data$fullname <- reorder(samp.data$fullname, rowSums(samp.data[-1]))

## Examine the new factor order
levels(samp.data$fullname)
attributes(samp.data$fullname)

Then just replot, using code from the original question

md <- melt(samp.data, id=(c("fullname")))
temp.plot<-ggplot(data=md, aes(x=fullname, y=value, fill=variable) ) + 
               geom_bar()+ 
               theme(axis.text.x=theme_text(angle=90)) + 
               labs(title = "Score Distribtion")
## ggsave(temp.plot,filename="test.png")