Adding legends to 3 plots in ggplot2

May 7, 2023

For a sample dataframe:

date = c("2021-2022", "2020-2021", "2019-2020", "2018-2019", "2017-2018", "2016-2017", "2015-2016", "2014-2015", "2013-2014", "2012-2013", "2011-2012")
cats = c(489701, 502743, 510776, 515904, 477746, 495208, 508466, 475334, 483368, 462693, 429065)
dogs = c(124046, 129445,132384, 140041, 68535, 64516, 63950, 60076, 59650, 59441, 56194)
pigs = c(91651, 85101, 78457, 63734, 45592, 43392, 40970, 38530, 37182, 36256, 34464)

df1 <- data.frame(date, cats, dogs, pigs)

I am trying to bar graph the cats data, and line graph the dogs and pig data.

So far I have:

p1<-ggplot(data=df1, aes(x=date, y=cats, colour = "cats")) +
  geom_bar(stat="identity") +
  theme(axis.text.x = element_text(angle = 60, vjust = 0.5)) +
  scale_y_continuous(labels = comma, 
                     limits=c(0,550000), 
                     name = "number") +
  labs(x = "Year") +
  geom_line(data = df1, aes(x=date, y=dogs), color = 'red', size = 0.75, group = 1) +
  geom_point(data = df1, aes(x=date, y=dogs), color = 'red', size = 1.5) +
  geom_line(data = df1, aes(x=date, y=pigs), color = 'blue', size = 0.75, , group = 1, linetype = "dashed") +
  geom_point(data = df1, aes(x=date, y=pigs), color = 'blue', size = 1.5)

p1

I am struggling to get a legend for the dogs and pigs line. I understand this is related to not having an appropriate aes characteristic – but how do I do this if I am already using color to set the line colour? (FYI – I don’t want the red outline but can’t seem to find what’s causing that).

I understand that part of my trouble is an untidy dataset, but I also had trouble converting it to a long dataset:

df2 <- pivot_longer(date, names_to = "animals", values_to = "count")
Error in UseMethod("pivot_longer") : 
  no applicable method for 'pivot_longer' applied to an object of class "character"

>Solution :

The issue is that to get a legend you have to map on aesthetics, i.e. instead of setting the line colors as arguments map on the color aes inside aes() and set your desired colors via scale_color_manual:

library(ggplot2)
library(scales)

ggplot(data = df1, aes(x = date)) +
  geom_col(aes(y = cats, fill = "cats")) +
  theme(axis.text.x = element_text(angle = 60, vjust = 0.5)) +
  scale_y_continuous(
    labels = comma,
    limits = c(0, 550000),
    name = "number"
  ) +
  labs(x = "Year") +
  geom_line(aes(y = dogs, color = "dogs"),
    size = 0.75, group = 1
  ) +
  geom_point(aes(y = dogs, color = "dogs"), size = 1.5) +
  geom_line(aes(y = pigs, color = "pigs"),
    size = 0.75, group = 1,
    linetype = "dashed"
  ) +
  geom_point(aes(y = pigs, color = "pigs"), size = 1.5) +
  scale_color_manual(values = c(pigs = "blue", dogs = "red"))