rotating axis labels in date format

Question

does anyone know how to rotate axis ticks in the date format with ggplot2? I want to get labels with "Date-Month" (ex. "1985-5") with a 45° angle on the x axis.

data sample:

Station Date Ptot
A 1980-02 16
A 1980-03 19
A 1980-04 40
A 1980-05 48
A 1980-06 NA
A 1980-07 18.5
A 1980-08 24.6
B 1980-07 50.8
B 1980-08 28.9
B 1980-09 32.9
B 1980-10 47.9
B 1980-11 16.3

I tried this:

library(ggplot2)
library(scales)

plot <- ggplot(data=na.omit(data), aes(x=Date, y=Ptot, group=Station))+
   geom_line()+
   facet_grid(Station~.)+
   scale_x_date(breaks = "year", labels=date_format("%Y-%m"))+
   xlab("Year")+
   ylab("Prec (mm)")+
   labs(colour = "Station")+
   theme(axis.text.x = element_text(angle = 45, hjust = 1))+
   theme_bw()

plot

but it doesn't work.

Thanks!

Answer 1

First, you should make column Date as date. As it do not have the day provided, you should add for example 01 to each date and convert them.

data$Date<-as.Date(paste(data$Date,"-01",sep=""),format="%Y-%m-%d")

To get correct placement of labels under x axis you should set not just angle= but also hjust=1 to ensure that end of the label is placed under the tick mark. Also theme_bw() should be placed before theme specification of axis texts.

ggplot(data=na.omit(data), aes(x=Date, y=Ptot, group=Station))+
  geom_line()+
  facet_grid(Station~.)+
  scale_x_date(breaks = "month", labels=date_format("%Y-%m"))+
  xlab("Year")+
  ylab("Prec (mm)")+theme_bw()+
  theme(axis.text.x = element_text(angle = 45, hjust = 1))