您说您希望绘图中总共有10行，每一年一行。但是，您的 Dataframe 中每一年的值都有多行（例如，在您提供的示例中，2013年有6行）。因此，听起来您想通过month和year对数据进行summarize，这可以使用dplyr包来完成。

library(tidyverse)
month <- rep(x = month.abb, times = 10)
emp <- sample(x = 12000:15000, size = 120, replace = TRUE)
year <- rep(2013:2022, times = 12)
new_df <- data.frame(month, emp, year) %>%
  mutate(year = factor(year)) %>% 
  mutate(month = factor(month))

# original plot
ggplot(new_df, aes(x = month, y = emp, group = 1, color = year)) + 
  geom_line()

# original plot with group changed to `year`, added geom_point
ggplot(new_df, aes(x = month, y = emp, group = year, color = year)) + 
  geom_line() + geom_point()

# summarized plot with geom_point
newer_df <- new_df %>%
  group_by(month, year) %>%
  summarize(emp_mean = mean(emp))

ggplot(newer_df, aes(x = month, y = emp_mean, group = year, color = year)) + 
  geom_line() + geom_point()