Specification of first and last tick marks with scale_x_date

Question

I would like to be able to specify the first and last tick marks which appear in a plot produced by ggplot2, but an running into some problems. Here is some code.

#Produce a vector of days 
dateVec <- seq(from = as.Date("2011-11-21"), to = as.Date("2012-11-23"), by = "days")

#Some random values
myData <- rnorm(length(dateVec))

# Plot it
qplot(dateVec, myData) + 
    scale_x_date(breaks = "4 weeks", limits = c(min(dateVec), max=max(dateVec))) + 
    theme(axis.text.x = element_text(size = 10, angle = 45, colour = "black",
          vjust = 1, hjust = 1))

Notice that the minimum date in the date vector is 2011-11-21 and the maximum date is 2012-11-23 and that I have specified the limits of the plot. However, the plot seems extended by some amount.

Is there a way to force the first and last tick marks to correspond to the actual limits specified in scale_x_date?

Thanks!

Answer 1

To ensure that axis is not expanded you can add argument expand = c(0, 0) to scale_x_date().

qplot(dateVec, myData) + 
scale_x_date(breaks = "4 weeks", limits = c(min(dateVec), max = max(dateVec)),
             expand=c(0,0)) +  
theme(axis.text.x  = element_text(size = 10, angle = 45, colour = "black",
      vjust = 1, hjust = 1))

UPDATE

If you need ticks that start with minimal and maximal dates then you can define your own breaks. For this I made vector break.vec containing minimal and maximal date as well as dates by month between them. Then used this vector to set breaks in scale_x_date().

break.vec <- c(as.Date("2011-11-21"),
               seq(from = as.Date("2011-12-01"), to = as.Date("2012-11-01"),
                 by = "month"),
               as.Date("2012-11-23"))

qplot(dateVec, myData) + 
  scale_x_date(breaks = break.vec) +  
  theme(axis.text.x = element_text(size = 10, angle = 45, colour = "black",
                                   vjust = 1, hjust = 1))