Add discrete labels to ggplot2 plot with continuous scale

Question

I am trying to add discrete labels to a ggplot2 plot with a continuous scale. While there are many questions using stat_function (i.e., about plotting multiple functions) and many about how to use different scales, I'm having trouble understanding how to change the scale in this specific instance.

Here is the plot:

myfun1 <- function(x) (13.076-96.543)*x + (-44.056 +102.057)*x^2 + (17.856 -42.996)*x^3 + (-2.996  + 7.444)*x^4 + (0.190 -0.450)*x^5 + 100.088 + 75.215 # average vs. lowest
myfun2 <- function(x) 13.076*x -44.056*x^2 + 17.856*x^3 -2.996*x^4 + 0.190*x^5 + 100.088 # lowest
myfun3 <- function(x) (13.076-183.093)*x + (-44.056 +229.447)*x^2 + (17.856 -99.353)*x^3 + (-2.996  + 17.517)*x^4 + (0.190 -1.080)*x^5 + 100.088 + 67.115 # highest vs. lowest

df <- data.frame(x = c(0, 6), y = c(0, 6))

myplot_weekday <- ggplot(data = df, aes(x = x, y = y)) + 
  stat_function(fun = myfun3, aes(color = "Highest")) +
  stat_function(fun = myfun2, aes(color = "Lowest")) +
  stat_function(fun = myfun1, aes(color = "Average")) +
  theme_minimal() +
  scale_colour_manual("Students' Course Grade", values = c("red", "black", "blue")) +
  theme(legend.position = "top") +
  theme(text=element_text(size= 14, family= "Times")) +
  ylab("Minutes of Videos Watched") +
  xlab("Weekday")

Instead of the continuous labels on the x-axis (0, 2, 4, and 6), I'm trying to add "Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", and "Saturday," but I sense I'm approaching this the wrong way.

Solution

You can set whatever breaks (which will get labels) and corresponding labels that you would like:

+ scale_x_continuous(breaks = 0:6,
    labels = paste0(c("Sun", "Mon", "Tues", "Wednes", "Thurs", "Fri", "Satur"), "day"))

Comments

[Joshua Rosenberg]

That is straightforward. This warning is displayed: Scale for 'x' is already present. Adding another scale for 'x', which will replace the existing scale. I ignored it, but it seems like when I save the plot, the original (i.e., 0, 2, 4, 6) scale is saved. Any tips about how to save the new (labeled) scale?

[Gregor Thomas]

Probably the warning is due to you having xlab() separately, better to add name = "Weekday" to scale_x_continuous and ditch the xlab. As for not saving, make sure you re-assign the plot object. If you just do my_plot_weekday + scale_x_cont... it will display without modifying the existing plot object. You need my_plot_weekday <- my_plot_weekday +... (or add it to the original definition and re-run the assignment).