Stop ggplot from reducing mulitple lines down to one line

Question

I am trying to make a figure where data are grouped into 10-year increments (e.g., 2000-2009, 2010-2019, 2020+) and have a common color among groups. I can set the color for individual years with no problem however, when I try to group years using a common color, the individual lines representing specific years get reduced down to one line. How can I stop this from happening?

suppressWarnings(library(tidyverse))

set.seed(333)

start_date <- as.Date('1990-01-01')
end_date <- as.Date('2023-12-31')
total_days <- as.numeric((end_date-start_date)+1)

# Create data frame
dat <- data.frame(
  Date = seq(start_date, end_date,'1 day'),
  Value = rnorm(total_days, 20, 4)
)

# add Year and day of year (DoY) to data frame
dat <- dat %>%
  mutate(Year = year(Date),
         DoY = yday(Date))

dat %>%
  ggplot(aes(x = DoY, y = Value, col = factor(Year))) +
  geom_line(data = subset(dat, Year == 2020), aes(colour = "2020")) +
  geom_line(data = subset(dat, Year == 2021), aes(colour = "2021")) +
  geom_line(data = subset(dat, Year == 2022), aes(colour = "2022")) +
  geom_line(data = subset(dat, Year == 2023), aes(colour = "2023")) +
  labs(x = 'Day of Year',
       y = 'Value',
       colour = 'Year Range') +
  scale_x_continuous(breaks = seq(1, 10, 1), limits = c(1,10)) +
  scale_color_manual(values = c("2020" = "#225ea8",
                                "2021" = "#41b6c4",
                                "2022" = "#a1dab4",
                                "2023" = "red")) +
  theme_bw()

# Why do all years >= 2020 get reduced down to one line?
# Each line (as in the figure above) should be red if the Year is >= 2020

dat %>%
  ggplot(aes(x = DoY, y = Value, col = factor(Year))) +
  # geom_line() +
  # geom_line(data = subset(dat, Year >= 1990 & Year <= 1999), aes(colour = "1990-1999")) +
  # geom_line(data = subset(dat, Year >= 2000 & Year <= 2009), aes(colour = "2000-2009")) +
  # geom_line(data = subset(dat, Year >= 2010 & Year <= 2019), aes(colour = "2010-2019")) +
  geom_line(data = subset(dat, Year >= 2020), aes(colour = "2020+")) +
  labs(x = 'Day of Year',
       y = 'Value',
       colour = 'Year Range') +
  scale_x_continuous(breaks = seq(1, 10, 1), limits = c(1,10)) +
  scale_color_manual(values = c("1990-1999" = "#225ea8",
                                "2000-2009" = "#41b6c4",
                                "2010-2019" = "#a1dab4",
                                "2020+" = "red")) +
  theme_bw()

^{Created on 2024-02-21 with reprex v2.0.2}

The ideal figure would have all the lines, as seen in the uppermost figure, be red without having to specify each year.

Answer 1

If I understand the request then just add Year as a grouping variable to the aes parameter to geom_line

 geom_line(data = subset(dat, Year >= 2020), aes(colour = "2020+", group=Year))