plotting line graph with two lines in R

Question

I'm trying to create a simple double line graph with a dataset I made. Here's the data:

date <- c("2021-04-06","2021-04-10", "2021-04-14", "2021-04-18")
as.Date(date)
graded <- c(3408, 3572, 3647, 3864)
psa10 <- c(2099, 2130, 2147, 2193)

graded_marvel <- data.frame(date, graded, psa10)
graded_marvel

And here's what I did to try and graph this

library("ggplot2")
graph <- ggplot(graded_marvel, aes(date)) +
  geom_line(aes(y = graded), color = "darkred") +
  geom_line(aes(y = psa10), color = "blue")

print(graph)

All I get is an empty graph that has the correct values on the axes, but the graph just comes up empty. Not sure what to do. Any help is appreciated!

Answer 1

This happens because your date variable is not a date, so ggplot2 interprets is as a character and assigns a discrete x scale. This auto-groups your data based on the x-axis value, so every 'group' only has one observations, with which you cannot draw a line. The way to fix this is to convert your date to a proper Date class.

library(ggplot2)

date <- c("2021-04-06","2021-04-10", "2021-04-14", "2021-04-18")
graded <- c(3408, 3572, 3647, 3864)
psa10 <- c(2099, 2130, 2147, 2193)

graded_marvel <- data.frame(date, graded, psa10)

ggplot(graded_marvel, aes(as.Date(date))) +
  geom_line(aes(y = graded), color = "darkred") +
  geom_line(aes(y = psa10), color = "blue")

^{Created on 2021-04-19 by the reprex package (v1.0.0)}

Answer 2

First get long format with pivot_longer . Then plot with ggplot2 .

library("ggplot2")
ggplot(df, aes(x=factor(date), y = values, group = names)) +
  geom_point(aes(color=names)) +
  geom_line(aes(linetype=names, color=names)) +
  scale_colour_manual(values=c("darkred", "blue"))

data:

df <- graded_marvel %>% 
  pivot_longer(
    cols = -date,
    names_to = "names",
    values_to = "values"
  )