year over year for daily time series with ggplot (hack)

yoy-plot.R

library(tidyverse)
library(lubridate)
# also uses quantmod, zoo, sfthemes, janitor

# less noisy
options("getSymbols.warning4.0" = FALSE)

# example daily time series for multiple years
goog_price <- quantmod::getSymbols(Symbols = "GOOG",
                                   auto.assign = FALSE) %>%
  zoo::fortify.zoo() %>% 
  as_tibble() %>% janitor::clean_names() %>%
  rename(date = index) %>%
  rename_with(~ str_remove(.x, "^goog_")) %>%
  mutate(year = as_factor(year(date)),
         doy = yday(date))

# doy to month start date, will be funky on leap years but w/e
doy_labels <- tibble(
  x = seq(as_date("2021-01-01"), 
          by = "month", length.out = 12),
  month_label = month(x, label = T),
  doy = yday(x)
)

yoy_goog_price <- goog_price %>% 
  filter(year(date) %in% 2019:2021) %>%
  ggplot(aes(doy, open,
             group = year,
             colour = year)) +
  geom_line() +
  scale_x_continuous(breaks = doy_labels$doy,
                     labels = doy_labels$month_label) +
  scale_y_continuous(labels = scales::dollar_format()) +
  labs(x = "Date", y = "Open Price",
       title = "Daily Google Open Price")

yoy_goog_price +
  sfthemes::theme_sf_light() +
  theme(
    axis.title.x = element_text(hjust=0.5),
    axis.title.y = element_text(hjust=0.5)
  )