boshek - 1 year ago 88
R Question

# Plotting a non-standard year (water year) with ggplot2

Building on this question and the use of "water year" in R I have question regarding plotting in ggplot2 with a common date axis over many years. A water year is definitely the start of the year to be October 1st ending September 30. It is a little more sensible for the hydrological cycle.

So say I have this data set:

``````library(dplyr)
library(ggplot2)
library(lubridate)

df <- data.frame(Date=seq.Date(as.Date("1910/1/1"), as.Date("1915/1/1"), "days"),
y=rnorm(1827,100,1))
``````

Then here is the wtr_yr function:

``````wtr_yr <- function(dates, start_month=10) {
# Convert dates into POSIXlt
dates.posix = as.POSIXlt(dates)
# Year offset
offset = ifelse(dates.posix\$mon >= start_month - 1, 1, 0)
# Water year
adj.year = dates.posix\$year + 1900 + offset
# Return the water year
}
``````

What I would like to do is use colour as a grouping variable, then make a x axes that only consists of month and date information. Usually I've done like so (using the lubridate package):

`````` ymd(paste0("1900","-",month(df\$Date),"-",day(df\$Date)))
``````

This works fine if year is arranged normally. However in this water year scenario, the real year span the water year. So ideally I'd like a plot that goes from October 1 to September 30 and plot separate lines for each water year maintaining all the correct water years. Here is where I am so far:

``````df1 <- df %>%
mutate(wtr_yrVAR=factor(wtr_yr(Date))) %>%
mutate(CDate=as.Date(paste0("1900","-",month(Date),"-",day(Date))))

df1 <- %>%
ggplot(aes(x=CDate, y=y, colour=wtr_yrVAR)) +
geom_point()
``````

So plotting that obviously date spans from Jan to Dec. Any ideas how I can force ggplot2 to plot these along the water year lines?

Here is a method that works:

``````df3 <- df %>%
mutate(wtr_yrVAR=factor(wtr_yr(Date))) %>%
#seq along dates starting with the beginning of your water year
mutate(CDate=as.Date(paste0(ifelse(month(Date) < 10, "1901", "1900"),
"-", month(Date), "-", day(Date))))
``````

Then:

``````df3 %>%
ggplot(., aes(x = CDate, y = y, colour = wtr_yrVAR)) +
geom_point() +
scale_x_date(date_labels = "%b %d")
``````

Which gives:

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