Missing legend on ggplot multi-line plot

Question

I'm ploting annual temperature data by year from a dataframe that contains the minimum, mean and maximum values for each year. I've been unable to get a legend on my plot. Ideally, the legend should have a Legend title and label the line colors as Min, Mean and Max.

Any help would be appreciated.

The data looks like (example) and the data is named "s":

Example data

The code:

ggplot(s, aes(Year)) + 
geom_line(aes(y=min), color="blue") +
geom_line(aes(y=mean), color="green") + 
geom_line(aes(y=max), color="red") + 
ggtitle("Fort Collins Mean Annual Temperature") + 
ylab("Temperature (degF)")

The Plot:

enter image description here

Please provide the data as plain text, not an image. You'll find this much easier with all the temperatures in one column and the type (min, mean, max) in another. — neilfws

neilfws neilfws · Accepted Answer · 2017-11-06T02:23:53

Here's some reproducible data that resembles yours:

set.seed(123)
df1 <- data.frame(Year = 1893:1903, 
                  min  = sample(-5:10, 11, replace = TRUE), 
                  mean = sample(50:70, 11, replace = TRUE), 
                  max  = sample(90:100, 11, replace = TRUE), 
                  n    = sample(150:350, 11, replace = TRUE))

If you gather the temperatures into one column and label them by type, the legend takes care of itself.

library(tidyverse)
df1 %>% 
  gather(measurement, value, -n, -Year) %>% 
  ggplot(aes(Year, value)) + 
    geom_line(aes(group = measurement, color = measurement)) +
    scale_x_continuous(breaks = 1893:1903) +
    labs(y = "Temperature (F)", title = "Fort Collins Annual Temperature") + 
    theme_bw()

Missing legend on ggplot multi-line plot

1 Answers