Adding legend to ggplot made from multiple data frames with controlled colors

Question

I have a ggplot2 line chart made from three data frames for which I have controlled the color scheme. I've instead used linetype to distinguish between lines. This leads to a situation in which a legend is not automatically generated. How can I create a legend for this plot?

tpAct <- data.frame(
  Date=seq.Date(as.Date('2017-09-01'), as.Date('2018-01-01'),by='month'),
  Reg1=rnorm(5, 10, 5),
  Reg2=rnorm(5, 15, 5),
  Reg3=rnorm(5, 20, 5),
  Reg4=rnorm(5, 25, 5),
  Reg5=rnorm(5, 30, 5),
  Total=rnorm(5, 60, 5)
)

tpOL <- data.frame(  
  Date=seq.Date(as.Date('2017-09-01'), as.Date('2018-01-01'),by='month'),
  Reg1=rnorm(5, 10, 5),
  Reg2=rnorm(5, 25, 5),
  Reg3=rnorm(5, 20, 5),
  Reg4=rnorm(5, 25, 5),
  Reg5=rnorm(5, 30, 5),
  Total=rnorm(5, 60, 5)
)

tpModL2 <- data.frame(  
  Date=seq.Date(as.Date('2017-09-01'), as.Date('2018-01-01'),by='month'),
  Reg1=rnorm(5, 10, 5),
  Reg2=rnorm(5, 25, 5),
  Reg3=rnorm(5, 20, 5),
  Reg4=rnorm(5, 25, 5),
  Reg5=rnorm(5, 30, 5),
  Total=rnorm(5, 60, 5)
)

ggplot() + 
  geom_line(data=tpAct, aes(x=Date, y=Reg1), color='red', size=1.25) +
  geom_line(data=tpAct, aes(x=Date, y=Reg2), color='blue', size=1.25) + 
  geom_line(data=tpAct, aes(x=Date, y=Reg3), color='green', size=1.25) + 
  geom_line(data=tpAct, aes(x=Date, y=Reg4), color='pink', size=1.25) + 
  geom_line(data=tpAct, aes(x=Date, y=Reg5), color='yellow', size=1.25) + 
  geom_line(data=tpAct, aes(x=Date, y=Total), color='black', size=1.25) + 
  geom_line(data=tpOL, aes(x=Date, y=Reg1), linetype=5, color='red', size=1.25) +
  geom_line(data=tpOL, aes(x=Date, y=Reg2), linetype=5, color='blue', size=1.25) +
  geom_line(data=tpOL, aes(x=Date, y=Reg3), linetype=5, color='green', size=1.25) +
  geom_line(data=tpOL, aes(x=Date, y=Reg4), linetype=5, color='pink', size=1.25) +
  geom_line(data=tpOL, aes(x=Date, y=Reg5), linetype=5, color='yellow', size=1.25) +
  geom_line(data=tpOL, aes(x=Date, y=Total), linetype=5, color='black', size=1.25) + 
  geom_line(data=tpModL2, aes(x=Date, y=Reg1), linetype=4, color='red', size=1.25) +
  geom_line(data=tpModL2, aes(x=Date, y=Reg2), linetype=4, color='blue', size=1.25) +
  geom_line(data=tpModL2, aes(x=Date, y=Reg3), linetype=4, color='green', size=1.25) +
  geom_line(data=tpModL2, aes(x=Date, y=Reg4), linetype=4, color='pink', size=1.25) +
  geom_line(data=tpModL2, aes(x=Date, y=Reg5), linetype=4, color='yellow', size=1.25) +
  geom_line(data=tpModL2, aes(x=Date, y=Total), linetype=4, color='black', size=1.25) +
  labs(x='', y='Total Balances ($B)')

Answer 1

Here's how to stack and plot the data using the sample data frames you provided:

library(tidyverse)

setNames(list(tpAct, tpOL, tpModL2), c("tpAct","tpOL","tpModL2")) %>% 
  map_df(~ .x %>% gather(key, value, -Date), .id="source") %>% 
  ggplot(aes(Date, value, colour=key, linetype=source)) +
    geom_line() +
    scale_colour_manual(values=c('red','blue','green','pink', 'yellow', 'black')) +
    theme_classic()

setNames(list(tpAct, tpOL, tpModL2), c("tpAct","tpOL","tpModL2")) puts the three data frames in a list and assigns the data frame names as the names of the list elements.

map_df(~ .x %>% gather(key, value, -Date), .id="source") converts the individual data frames to long format and stacks them into a single long-format data frame.

Here's what the plot looks like:

A faceted plot might be easier to read:

setNames(list(tpAct, tpOL, tpModL2), c("tpAct","tpOL","tpModL2")) %>% 
  map_df(~ .x %>% gather(key, value, -Date), .id="source") %>% 
  ggplot(aes(Date, value, colour=key)) +
    geom_line() +
    scale_colour_manual(values=c('red','blue','green','pink', 'yellow', 'black')) +
    theme_classic() +
    facet_grid(~ source)

Answer 2

When you find yourself wanting to manually add a legend with ggplot2 , I've found it usually means you're going about making your plot in a way other than what ggplot2 intended.

To get ggplot to generate a legend for this plot, you need to reshape your data into a long format with groups before giving it to ggplot .

You'll want to combine all three data sets (tpAct(), tpOL(), tpModL2() - I'm assuming that these are functions that are returning data frames) into a single data.frame -- let's call this combineddata. The columns would then be: dataset (to denote which set the observation is from), Date, RegType (Reg1, Reg2,..Total), and Value (the actual y values you're plotting).

Then you could create a plot with something like the following:

ggplot(combineddata, aes(x=Date, y=Value, color=RegType, linetype=dataset) + 
    geom_line()

This will draw one line for each combination of regression and data set like you have above, but will do so automatically and create a legend. If you don't like the colors and line types that ggplot picks for you, you can further specify the specific colors and line types you want to use with scales:

ggplot(combineddata, aes(x=Date, y=Value, color=RegType, linetype=dataset) + 
    geom_line() +
    scale_color_manual(values = c("red", "blue", "green", "pink", "yellow", "black")) + 
    scale_linetype_manual(values = c(1, 5, 4)

You may need to explicitly make RegType and dataset ordered factors before sending the data to ggplot to get them in the correct order, or change the order of the colors and line types above.