Adding labels to a line plot with ggplot2

Question

I am trying to add like a legend on the right that indicates the variable name. In the data frame, the lines are columns named "Correctional Spending" or "Medicaid Spending", and I want those to be shown. Can someone help please?

Here is my plot:

Here is my code:

ggplot(Alabama, aes(x=AlYear)) + 
  geom_line(aes(y = AlMed), color = "darkred") + 
  geom_line(aes(y = AlCorr), color="steelblue", linetype="twodash") +
  labs(title='Figure 3: Alabama Social Spending',
        x='Fiscal Year', y= 'Spending (in $100,000')

Answer 1

This is because the type of spending (Coor or Med) is actually a variable, that you want to map to the color aesthetic. So, you should first pivot_longer() the data, to keep them in a column, then you should include it as a variable inside the aes(). Finally, since the color is now a variable, you can set manual values in the corresponding scale.

library(tidyverse)
Alabama <- tibble(AlYear = 2010:2015,
                  AlMed = c(300,400,600,650,700,750),
                  AlCorr = c(400,400,450,500,450,450))

Alabama %>%
  pivot_longer(AlMed:AlCorr, names_to = "Spending Type") %>%
  ggplot(aes(x=AlYear, y = value, color= `Spending Type`)) + 
  geom_line() + 
  labs(title='Figure 3: Alabama Social Spending',
       x='Fiscal Year', y= 'Spending (in $100,000') +
  scale_color_manual(values=c("darkred", "steelblue"),
                     labels = c("Medicaid Spending","Correctional Spending"))

^{Created on 2020-12-09 by the reprex package (v0.3.0)}

Of course, you can do the same thing for the linetype (add it in the aes() call, and add a scale_linetype_manual() at the end).