Discrete values and geom_ribbon and geom_lines + problems with "discrete" scale

Question

I have got a file like this one:

Month,Open,Closed
2017-08,53,38
2017-09,102,85
2017-10,58,38
2017-11,51,42
2017-12,32,24
2018-01,24,30
2018-02,56,46
2018-03,82,74
2018-04,95,89
2018-05,16,86

I want to plot both lines, and also shade the difference between them. So this works:

ggplot()  +geom_line(data=issues.m,aes(x=Month,y=Open,group=1))
 +geom_line(data=issues.m,aes(x=Month,y=Closed,group=1)) 
 +geom_ribbon(data=issues.m, aes(x=Month,ymin=Closed,ymax=Open,color=Open-Closed))
 +theme_tufte() 
 +theme(axis.text.x = element_text(angle = 90, hjust = 1))

producing this

First problem here is that I would like the whole area between the two lines shaded if possible, not a single line. How can I do that?

But I would also like to color the two lines. If I add a color to one of them:

ggplot() 
 +geom_line(data=issues.m,aes(x=Month,y=Open,group=1,color='open')) 
 +geom_line(data=issues.m,aes(x=Month,y=Closed,group=1)) 
 +geom_ribbon(data=issues.m, aes(x=Month,ymin=Closed,ymax=Open,color=Open-Closed))
 +theme_tufte() 
 +theme(axis.text.x = element_text(angle = 90, hjust = 1))

I get the error:

Error: Continuous value supplied to discrete scale

So, can what I want to do be done at all? Would it be possible to change the colour palette of the ribbon too?

Basically you want two independent color scales? Right now you are trying to make two - one indicating the difference between open and closed, and one indicating if its Open or Closed — Jack Brookes, May 31 '18 at 18:18
Can you also fix the formatting, put each `+ geom...` on a new line — Jack Brookes, May 31 '18 at 18:20
@JackBrookes I would simply like the lines to have different color. — jjmerelo, May 31 '18 at 18:26
Not quite a duplicate, but we had a similar post about a week ago here: https://stackoverflow.com/questions/50544765/plot-ggplot-smooth-color-area-between-2-curves/50545516 — camille, May 31 '18 at 18:29
Dont map the string "open" to the aesthetic scale, apply the layer parameter directly: `+geom_line(data=issues.m, aes(x=Month,y=Open,group=1), color = "red")` — Jack Brookes, May 31 '18 at 18:33

score 1 · Accepted Answer · answered Jun 01 '18 at 02:03

Your error was because you were mapping Open - Closed onto the color, which will be a continuous variable, i.e. the difference between those two values for each month. But you also assigned "open" to color inside the aes in one of your geom_lines. That means you're trying to assign both continuous values and discrete values to the same scale, and that's not going to work.

If all you need to do is get 2 colors, one for each line, you can do this one of two ways, the second of which fits more into the ggplot/tidyverse way of doing things.

First off I turned your dates into date objects to clean up the x-axis and avoid rotating the labels—feel free to experiment with the date breaks that work well in scale_x_date.

The less "tidy" way is to just make two geom_lines, one for Open and one for Closed, and assign a color to each.

library(tidyverse)


df_dated <- df %>%
  mutate(month2 = sprintf("%s-01", Month) %>% lubridate::ymd())

ggplot(df_dated, aes(x = month2)) +
  geom_ribbon(aes(ymin = Open, ymax = Closed), fill = "lightblue2") +
  geom_line(aes(y = Open), color = "green3") +
  geom_line(aes(y = Closed), color = "red") +
  ggthemes::theme_tufte()

But the more idiomatically "tidy" way is to make a long-shaped version of the data so you can map a variable—in this case whether an observation is the opening or closing value—onto an aesthetic such as color. This also gives you a legend—if you don't want it, you can get rid of it in the theme. This lets you set a scale for the colors, instead of hard-coding into each geom_line.

df_date_long <- df_dated %>%
  gather(key, value, -month2, -Month)

ggplot(df_dated, aes(x = month2)) +
  geom_ribbon(aes(ymin = Open, ymax = Closed), fill = "lightblue2") +
  geom_line(aes(y = value, color = key), data = df_date_long) +
  scale_color_manual(values = c(Open = "green3", Closed = "red")) +
  ggthemes::theme_tufte()

Discrete values and geom_ribbon and geom_lines + problems with "discrete" scale

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