Changing Date Labels From Odd to Even Years

Question

I want to make a seemingly trivial adjustment to the chart pictured below:

I would like the labels along the x-axis to be even years, rather than odd years. So instead of going from 2009 -> 2011 -> 2013, they should go from 2008 -> 2010 -> 2012, and so forth...

How do I go about doing this?

Here is the code:

germany_yields <- read.csv(file = "Germany 10-Year Yield Weekly (2007-2020).csv", stringsAsFactors = F)
italy_yields <- read.csv(file = "Italy 10-Year Yield Weekly (2007-2020).csv", stringsAsFactors = F)

germany_yields <- germany_yields[, -(3:6)]
italy_yields <- italy_yields[, -(3:6)]

colnames(germany_yields)[1] <- "Date"
colnames(germany_yields)[2] <- "Germany.Yield"
colnames(italy_yields)[1] <- "Date"
colnames(italy_yields)[2] <- "Italy.Yield"

combined <- join(germany_yields, italy_yields, by = "Date")
combined <- na.omit(combined)
combined$Date <- as.Date(combined$Date,format = "%B %d, %Y")
combined["Spread"] <- combined$Italy.Yield - combined$Germany.Yield

fl_dates <- c(tail(combined$Date, n=1), head(combined$Date, n=1))

ggplot(data=combined, aes(x = Date, y = Spread)) + geom_line() +

       scale_x_date(limits = fl_dates, 
                    expand = c(0, 0), 
                    date_breaks = "2 years",
                    date_labels = "%Y")

Answer 1

A -- not very elegant -- way would be to put these arguments in your scale_x_date() :

scale_x_date(date_labels = "%Y", 
             breaks = ymd(unique(year(combined$fl_dates)[year(combined$fl_dates)%%2 == 0]), truncated = 2L)

(we define breaks manually, by subsetting the whole range of dates and keeping the even years)

Answer 2

That's actually fairly simple. Just set the lower limit to an even number, and set the upper limit to NA . As you haven't provided a reproducible example, here on some fake data.

library(tidyverse)

mydates <- seq(as.Date("2007/1/1"), by = "3 months", length.out =100)

df <- tibble(
  myvalue = rnorm(length(mydates))
)

# without limits argument

ggplot(df ) +
  aes(x = mydates, y = myvalue) +
  geom_line(size = 1L, colour = "#0c4c8a") +
  scale_x_date(date_breaks = "2 years",
               date_labels = "%Y")

# with limits argument 

ggplot(df ) +
  aes(x = mydates, y = myvalue) +
  geom_line(size = 1L, colour = "#0c4c8a") +
  scale_x_date(date_breaks = "2 years",
               date_labels = "%Y",
               limits = c(as.Date("2006/1/1"), NA))

^{Created on 2020-04-29 by the reprex package (v0.3.0)}