ggplot legend - scale_colour_manual not working

Question

I am trying to add a legend to my graphs, but nothing ever shows up. This is the code I have:

ggplot(main, aes(x = ceiling(session/2))) + 
geom_line(aes(y = C_overall), colour = "blue", stat = "summary", fun.y = "mean") +
geom_line(aes(y = I_overall), colour = "red", stat = "summary", fun.y = "mean") +
labs(title = 'Overall Accuracy', x = 'Session', y = 'Percent Accurate') +
facet_wrap(~bird)

This shows me what I want, except with no legend. Everything I've seen says to use scale_colour_manual like this:

ggplot(main, aes(x = ceiling(session/2))) + 
geom_line(aes(y = C_overall), colour = "one", stat = "summary", fun.y = "mean") +
geom_line(aes(y = I_overall), colour = "two", stat = "summary", fun.y = "mean") +
labs(title = 'Overall Accuracy', x = 'Session', y = 'Percent Accurate') +
facet_wrap(~bird) +
scale_colour_manual(name = 'Congruency', values = c("one" = "blue", "two" = "red"))

This seems to work for everyone else, but R just tells me that 'one' is an invalid color name. I've worked on this for hours and I'm nowhere closer to figuring this out.

Here is some of my data if it's helpful:

bird   session  C_overall   I_overall
23W     1       42.5        42.5
23W     2       46.25       47.5
23W     3       51.25       57.5
23W     4       47.5        52.5
23W     5       47.5        52.5
23W     6       47.5        62.5
23W     7       52.5        52.5
23W     8       50          55
23W     9       51.25       52.5
23W     10      48.75       47.5
43R     1       47.5        42.5
43R     2       43.75       37.5
43R     3       58.75       40
43R     4       51.25       40
43R     5       51.25       52.5
43R     6       36.25       35
43R     7       53.75       40
43R     8       57.5        45
43R     9       61.25       52.5
43R     10      48.75       47.5
57Y     1       45          67.5
57Y     2       53.75       62.5
57Y     3       47.5        65
57Y     4       52.5        52.5
57Y     5       47.5        50
57Y     6       48.75       70
57Y     7       66.25       72.5
57Y     8       55          60
57Y     9       57.5        72.5
57Y     10      58.75       67.5
76B     1       51.25       50
76B     2       56.25       42.5
76B     3       60          60
76B     4       68.75       70
76B     5       73.75       75
76B     6       55          52.5
76B     7       68.75       62.5
76B     8       40          40
76B     9       57.5        55
76B     10      66.25       70

The blue line should be "Congruent" and the red line should be "Incongruent".

Any help about how to make a legend would be greatly appreciated! Thanks in advance!!

Answer 1

I would convert the data into long format before plotting:

library(reshape2)

main <- melt(main, c("bird", "session"))

ggplot(main, aes(x=ceiling(session/2), y=value, color=variable)) + 
  geom_line(stat="summary", fun.y="mean", size=1) +
  labs(title="Overall Accuracy", x="Session", y="Percent Accurate") +
  facet_wrap(~ bird) +
  scale_color_discrete("Results", labels=c("Congruent", "Incongruent"))

Would that work for you?

Answer 2

Make following changes in geom_line s and scale_color_discrete and you are good to go.

ggplot(main, aes(x = ceiling(session/2))) + 
## changes in line below
geom_line(aes(y = C_overall, colour = "Congruent"), stat = "summary", fun.y = "mean") +
## changes in line below
geom_line(aes(y = I_overall, colour = "Incongruent"), stat = "summary", fun.y = "mean") +
labs(title = 'Overall Accuracy', x = 'Session', y = 'Percent Accurate') +
facet_wrap(~bird) +
# changes in line below
scale_color_discrete("Congruency")