Plot separate years on a common day-month scale

Question

I want to create a time series plot of temperatures for the summers of 2012 and 2013.

The only problem is that I want the data series to plot one on top of the oth

Answer 1

If you want to plot both years in the same plot above each other then use dayMo as your x values (they don't have to be date object).

df$dayMo<-c("06-01", "07-01","08-01","09-01","06-01", "07-01","08-01","09-01")
ggplot(df, aes(dayMo, temp, color=year))+
  geom_point()

Answer 2

If your base dataset is temp and date, then this avoids manipulating the original data frame:

ggplot(df) +
  geom_point(aes(x=strftime(date,format="%m-%d"),
                 y=temp, 
                 color=strftime(date,format="%Y")), size=3)+
  scale_color_discrete(name="Year")+
  labs(x="date")

EDIT (Response to OP's comment).

So this combines the approach above with Henrik's, using dates instead of char for the x-axis, and avoiding modification of the original df.

library(ggplot2)
ggplot(df) +
  geom_point(aes(x=as.Date(paste(2014,strftime(date,format="%m-%d"),sep="-")),
                 y=temp, 
                 color=strftime(date,format="%Y")), size=3)+
  scale_color_discrete(name="Year")+
  labs(x="date")

Answer 3

Another possibility is to create a fake date where a single year is concatenated with month and day from the original 'date'. An x variable of class Date is easy to format with scale_x_date. Load scales package to access nice breaks and formatting functions: labels = date_format(); breaks = date_breaks(). See strptime for other date formats.

library(scales)

df$date2 <- as.Date(paste(2014, format(date, "%m-%d"), sep = "-"))

ggplot(df, aes(date2, temp, color = year)) +
  geom_point() +
  scale_x_date(labels = date_format("%m/%d"))

ggplot(df, aes(date2, temp, color=year)) +
  geom_point() +
  scale_x_date(labels = date_format("%b-%d"),
               breaks = date_breaks("months"))