Can't get graph colours/legend to work with double y-axis?-CodePudding

ggplot(modified)  
  geom_line(aes(Month, BrentSpot))  
  geom_line(aes(Month, CPI, colour = 'green'))  
  theme_minimal()  
  scale_y_continuous(
    "Brent Spot Price", 
    sec.axis = sec_axis(~ . * 1.1, name = "CPI")
  )

This code produces a black line for BrentSpot and a red line for CPI ? When I add more lines/variables to the graph none of the colours match up.

CodePudding user response：

I created a sample dataset:

modified <- data.frame(Month = c(1, 2, 3, 4, 5, 6),
                       BrentSpot = c(1, 3, 2, 4, 5, 2),
                       CPI = c(2, 4, 3, 1, 5, 6))

Output:

  Month BrentSpot CPI
1     1         1   2
2     2         3   4
3     3         2   3
4     4         4   1
5     5         5   5
6     6         2   6

You can add colors to the scale_color_manual. You can use this code:

ggplot(modified)  
  geom_line(aes(Month, BrentSpot, colour = "Brent"))  
  geom_line(aes(Month, CPI, colour = "CPI"))  
  theme_minimal()  
  scale_y_continuous(
    "Brent Spot Price", 
    sec.axis = sec_axis(~ . * 1.1, name = "CPI")
  )  
  scale_color_manual(values=c("#CC6666", "#9999CC"))

Output:

CodePudding user response：

It looks as though your data is in long format, with the price variable split across multiple columns (BrentSpot and CPI).

When this is the case and you want a legend, you need to give each line a colour mapping inside aes.

I have created a data set (see below) that should hopefully match yours in terms of names and column types to demonstrate:

library(ggplot2)

ggplot(modified)  
  geom_line(aes(Month, BrentSpot, colour = "Brent"))  
  geom_line(aes(Month, CPI, colour = 'CPI'))  
  theme_minimal()  
  scale_color_manual(values = c("red4", "green4"))  
  scale_y_continuous(
    "Brent Spot Price", 
    sec.axis = sec_axis(~ . * 1.1, name = "CPI")
  )

Data

set.seed(1)

modified <- data.frame(Month     = seq(as.Date("2020-01-01"), 
                                       as.Date("2021-12-01"),
                                       by = "month"),
                       BrentSpot = cumsum(rnorm(24))   100,
                       CPI       = cumsum(rnorm(24))   100)