Change colour of line in ggplot2 in R based on a category

August 14, 2024

i have the following data frame in R

A tibble: 24 × 4
   answers  Year Categories Satisfaction
   <chr>   <dbl> <chr>             <dbl>
 1 A        2019 Football           46.7
 2 A        2019 Basket             20.7
 3 A        2019 Volley             36.5
 4 A        2020 Football           43.7
 5 A        2020 Basket             21  
 6 A        2020 Volley             31.2
 7 A        2022 Football           49  
 8 A        2022 Basket             17.9
 9 A        2022 Volley             34.2
10 A        2023 Football           33.8

which its structure in R is the following:

df = structure(list(answers = c("A", "A", "A", "A", "A", "A", "A", 
"A", "A", "A", "A", "A", "B", "B", "B", "B", "B", "B", "B", "B", 
"B", "B", "B", "B"), Year = c(2019, 2019, 2019, 2020, 2020, 2020, 
2022, 2022, 2022, 2023, 2023, 2023, 2019, 2019, 2019, 2020, 2020, 
2020, 2022, 2022, 2022, 2023, 2023, 2023), Categories = c("Football", 
"Basket", "Volley", "Football", "Basket", "Volley", "Football", 
"Basket", "Volley", "Football", "Basket", "Volley", "Tennis", 
"Hockey", "Other", "Tennis", "Hockey", "Other", "Tennis", "Hockey", 
"Other", "Tennis", "Hockey", "Other"), Satisfaction = c(46.7, 
20.7, 36.5, 43.7, 21, 31.2, 49, 17.9, 34.2, 33.8, 30.1, 33.2, 
68.7, 68.7, 68.7, 69.7, 70.2, 70.2, 66.8, 72.7, 72.7, 76.1, 75.4, 
75.4)), row.names = c(NA, -24L), class = c("tbl_df", "tbl", "data.frame"
))

i have grouped the plot using ggplot2 as follows and as the picture shows. But I want to change the colours of the lines.If it the A group the line to be green and if is group B to be red. How can i do it in R ?

P2 = ggplot(df, aes(x = Year, y = Satisfaction, color = factor(Categories), group = Categories)) +
  geom_line(aes(color = ifelse(answers == "Unfavorable", "darkred", "forestgreen"))) +
  geom_point(size = 2) +
  facet_grid(Categories ~ answers, scales = "free_y") +
  theme_minimal() +
  labs(
    x = "Year",
    y = "Satisfaction",
    color = "Categories") +
  # theme(axis.text.x = element_text(angle = 45, hjust = 1))+
  theme(axis.text.x = element_text(angle = 45, hjust = 1),
        strip.background = element_rect(fill = "lightgrey"), # Add background color to facet labels
        strip.text = element_text(size = 12, face = "bold"), # Enhance facet label text
        panel.spacing = unit(1, "lines")) + # Increase spacing between facets
  geom_text(aes(label = paste(Satisfaction,"%") ), nudge_x = 0.1,color="black")+
  theme(legend.position = "none")
P2

>Solution :

If a legend is not required you can easily achieve your desired result by wrapping the if_else you use to conditionally assign the color in I() aka AsIs which however requires ggplot2 >= 3.5.0. Doing so you can still map a different variable on the color as for your points without the need to specify a separate color scale.

library(ggplot2)

packageVersion("ggplot2")
#> [1] '3.5.1'

ggplot(df, aes(
  x = Year, y = Satisfaction,
  color = factor(Categories), group = Categories
)) +
  geom_line(
    aes(color = I(ifelse(answers == "A", "darkred", "forestgreen")))
  ) +
  geom_point(size = 2) +
  facet_grid(Categories ~ answers, scales = "free_y") +
  theme_minimal() +
  labs(
    x = "Year",
    y = "Satisfaction",
    color = "Categories"
  ) +
  theme(
    axis.text.x = element_text(angle = 45, hjust = 1),
    strip.background = element_rect(fill = "lightgrey"),
    strip.text = element_text(size = 12, face = "bold"),
    panel.spacing = unit(1, "lines")
  ) +
  geom_text(
    aes(label = paste(Satisfaction, "%")),
    nudge_x = 0.1, color = "black"
  ) +
  theme(legend.position = "none")