line graph of four variables in r in just one plot

July 26, 2022

I would like to create a line graph that shows how the trend of five air pollutants were during the years 2009 to 2019.

Year	CO2	NO2	O3	PM2.5
2009	30	18	20	30
2010	32	16	22	20
2011	33	16	24	20
2012	32	15	25	22
2013	34	14	27	24
2014	36	14	28	22
2015	38	13	29	20
2016	39	13	30	18
2017	40	12	32	16
2018	44	13	34	15
2019	45	11	38	14

I gave that code but it is a histogram, i would like to have a line graph were all four are in the same plot.

df %>%
  ggplot(aes(x = Year, y = n, fill = airpollutants)) +
  geom_col() +
  facet_wrap(~Year)  + ggtitle("trend of airpollutants")

I want this output:
https://cdn.ablebits.com/_img-blog/line-graph/line-graph-excel.png

>Solution :

set.seed(123)
library(ggplot2)
library(tidyr)

# Example data
df <- data.frame(year = 2009:2019,
                 CO2 = sample(30:40, 11),
                 NO2 = sample(10:20, 11),
                 O3 = sample(20:30, 11),
                 PM2.5 = sample(15:25, 11))

# Convert to long format
df_long <- pivot_longer(df, 
                        cols = c(CO2, NO2, O3, PM2.5), 
                        values_to = "Concentration",
                        names_to = "Pollutant")


# Plot
ggplot(df_long,
       aes(
         x = year,
         y = Concentration,
         color = Pollutant,
         linetype = Pollutant
       )) +
  geom_line(size = 0.7) +
  ggtitle("Trend of Airpollutants") +
  xlab("Year") +
  ylab("Concentration") +
  scale_x_continuous(breaks = seq(2009, 2019, by = 1), limits = c(2009,2019)) +
  theme_minimal()