You can use the following basic syntax to order the y-axis labels alphabetically in ggplot2:

#sort y-axis variable in alphabetical order
df$y_var<- factor(df$y_var, levels=rev(sort(df$y_var)))

#create scatter plot with y-axis in alphabetical order
ggplot(df, aes(x=x_var, y=y_var)) + 
  geom_point()

The following example shows how to use this syntax in practice.

Example: Order Y-Axis Labels Alphabetically in ggplot2

Suppose we have the following data frame in R that shows the points scored by various basketball teams:

#create data frame
df <- data.frame(team=c('B', 'D', 'E', 'F', 'A', 'C', 'H', 'G'),
                 points=c(22, 12, 10, 30, 12, 17, 28, 23))

#view data frame
df

  team points
1    B     22
2    D     12
3    E     10
4    F     30
5    A     12
6    C     17
7    H     28
8    G     23

If we create a scatter plot with points on the x-axis and team on the y-axis, ggplot2 will automatically display the teams in alphabetical order (starting from the bottom):

library(ggplot2)

#create scatter plot
ggplot(df, aes(x=points, y=team)) + 
  geom_point(size=2)

Notice that the labels on the y-axis are in alphabetical order from A to Z, starting from the bottom.

To arrange the y-axis labels in reverse alphabetical order, we can use the following code:

library(ggplot2)

#sort y-axis variable in alphabetical order
df$team<- factor(df$team, levels=rev(sort(df$team)))

#create scatter plot with y-axis in alphabetical order
ggplot(df, aes(x=points, y=team)) +
  geom_point()

Notice that the labels on the y-axis are now in reverse alphabetical order, starting from the bottom.

The following tutorials explain how to perform other common tasks in ggplot2: