Can't add legend to ggplot2 figure – scale_color_manual() does nothing

November 23, 2021

The below is fully reproducible. I have the data frame

Deciles    P_pred      P_true
1          0.3366666   0.2586773
2          0.3531208   0.3151918
3          0.3692757   0.3379759
4          0.3898140   0.3886151
5          0.4183384   0.4487537
6          0.4577579   0.5008214
7          0.5134715   0.5796729
8          0.5940276   0.6359546
9          0.7087249   0.7242340
10         0.8592295   0.8133705

I want to plot both P_pred and P_true on the y-axis against Deciles in the same figure and add a legend as well. This is what I did

ggplot(data = averages, aes(x = as.integer(Deciles))) +
  scale_x_reverse(breaks = 10:1) +
  geom_line(aes(y = P_pred), color = 'darkred', size = 2) + 
  geom_line(aes(y = P_true), color = 'darkgreen', size = 2) +
  ylab('Probabilities') + 
  xlab('Deciles') +
  scale_color_manual(values = c('darkred','darkgreen'))

However, the legend is not appearing. What am I doing wrong?

>Solution :

Move the color to your aes() and it works as expected

ggplot(data = averages, aes(x = as.integer(Deciles))) +
  scale_x_reverse(breaks = 10:1) +
  geom_line(aes(y = P_pred, color = 'darkred'), size = 2) + 
  geom_line(aes(y = P_true, color = 'darkgreen'), size = 2) +
  ylab('Probabilities') + 
  xlab('Deciles') +
  scale_color_manual(values = c('darkred','darkgreen'))