Add legend to multiple time-series plot using ggplot

Question

I have two time series data that I want to show on the same graph. Both series have three columns: Date, County and Value. Here is my code:

#Data
Series1 <- data.frame(Date = c(2000,2001,2000,2001), County = c("a", "a", "b", "b"),Total = c(100,150,190,130))
Series2 <- data.frame(Date = c(2000,2001,2000,2001), County = c("a", "a", "b", "b"),Total = c(180,120,140,120))

#Plot data
ggplot() + 
    geom_line(data = Series1, aes(x = Date, y = Total, color = County), linetype="solid") +
    geom_line(data = Series2, aes(x = Date, y = Total, color = County), linetype="dashed")

The plot looks like this:

Now I just need to add one legend showing that solid line represents Series1 and dashed line represents Series2. How can I do this?

Possible duplicate of [R: changing-the-line-type-in-the-ggplot-legend](http://stackoverflow.com/questions/14875582/changing-the-line-type-in-the-ggplot-legend) — PereG, Jan 08 '16 at 15:30
Possible duplicate of [R: legend with points and lines being different colors (for the same legend item)](http://stackoverflow.com/questions/19053440/r-legend-with-points-and-lines-being-different-colors-for-the-same-legend-item) — aosmith, Jan 08 '16 at 16:58
@PereG I tried +scale_linetype_manual("Type",values=c("solid"=2,"dashed"=1)), but nothing happen. — Sean, Jan 08 '16 at 19:54
@Sean if you provide a minimum reproducible example, it would be much easier to help — PereG, Jan 08 '16 at 20:05
@PereG I added a small subset of my data as example, hope it will help. TIA. — Sean, Jan 08 '16 at 21:17

score 1 · Accepted Answer · answered Jan 08 '16 at 21:28

1

Legends are created automatically when you use aes() to map a data column to an aesthetic. You don't have a data column that you're mapping to the linetype aesthetic, so we need to create one.

Series1$series = 1
Series2$series = 2
all_series = rbind(Series1, Series2)

Now we've all the data together and plotting is easy:

ggplot(all_series,
       aes(x = Date, y = Total, color = County, linetype = factor(series))) + 
    geom_line()

Automatic legend, only one geom_line call, using ggplot as it's meant to be used: with tidy data.

answered Jan 08 '16 at 21:28

Gregor Thomas

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I agree with Gregor that the right thing is to manipulate the data previously. – PereG Jan 08 '16 at 21:47
Thank you both @PereG@Gregor. It works well. My follow-up question is: When I made a bunch of figures, sometimes the "County" legend box comes first and sometimes the "Series" legend box does. Is there a way to make them consistent? – Sean Jan 11 '16 at 15:43
Explicitly define it using an `order` argument to `guide_legend` as shown here: http://stackoverflow.com/a/11397958/903061. And do make a habit of searching for answers before asking. This was the first hit searching Stack Overflow for "ggplot2 order legends". – Gregor Thomas Jan 11 '16 at 17:09

PereG · Answer 2 · 2016-01-08T21:50:27.543

1

You are really close...

ggplot() + 
      geom_line(data = Series1, aes(x = Date, y = Total, color = County), linetype="solid") +
      geom_line(data = Series2, aes(x = Date, y = Total, color = County), linetype="dashed")+ scale_linetype_manual()

edited Jan 08 '16 at 21:50

answered Jan 08 '16 at 21:43

PereG

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Add legend to multiple time-series plot using ggplot

2 Answers2