How do I manually change the key labels in a legend in ggplot2

Question

I am preparing a plot for publication. I created a stacked box plot to show frequency of patients in each group who were some complicated accumulation of seronegatives versu

Answer 1

The standard way is to use the scale functions to change the displayed labels for groups. You can replace your ggplot call with

ggplot(data, aes(grp, fill=outcome)) + geom_bar() +xlab("group") +
  ylab("number of subjects") + 
  scale_fill_discrete("Serologic response", 
                      breaks=c("(10.1,79.9]","(79.9,150]"), 
                      labels=c("double negative", "positive for a and/or b"))

Note that the scale's title has been incorporated into the scale_fill_discrete call. You can do this with the axes too, if you like

ggplot(data, aes(grp, fill=outcome)) + geom_bar() +
  scale_x_discrete("group") +
  scale_y_continuous("number of subjects") + 
  scale_fill_discrete("Serologic response", 
                      breaks=c("(10.1,79.9]","(79.9,150]"), 
                      labels=c("double negative", "positive for a and/or b"))