How to Create a GGPlot with Multiple Lines

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31 Dec

How to Create a GGPlot with Multiple Lines

Alboukadel

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ggplot2

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This tutorial describes how to create a ggplot with multiple lines.

Related Book

GGPlot2 Essentials for Great Data Visualization in R

Load ggplot2 package

Load ggplot2 and set the default theme:

library(ggplot2)
theme_set(theme_minimal())

Data

The US economics time series datasets are used. This is a data frame with 478 rows and 6 variables.

head(economics)
## # A tibble: 6 x 6
##   date         pce    pop psavert uempmed unemploy
##   <date>     <dbl>  <int>   <dbl>   <dbl>    <int>
## 1 1967-07-01  507. 198712    12.5     4.5     2944
## 2 1967-08-01  510. 198911    12.5     4.7     2945
## 3 1967-09-01  516. 199113    11.7     4.6     2958
## 4 1967-10-01  513. 199311    12.5     4.9     3143
## 5 1967-11-01  518. 199498    12.5     4.7     3066
## 6 1967-12-01  526. 199657    12.1     4.8     3018
  • date: Month of data collection
  • psavert: personal savings rate
  • pce: personal consumption expenditures, in billions of dollars
  • unemploy: number of unemployed in thousands
  • uempmed: median duration of unemployment, in weeks
  • pop: total population, in thousands

Basic line plot

Line plot of the variable ‘psavert’ by date:

ggplot(data = economics, aes(x = date, y = psavert))+
  geom_line()

Plot with multiple lines

Well plot both ‘psavert’ and ‘uempmed’ on the same line chart.

  • Solution 1: Make two calls to geom_line():
ggplot(economics, aes(x=date)) + 
  geom_line(aes(y = psavert), color = "darkred") + 
  geom_line(aes(y = uempmed), color="steelblue", linetype="twodash")

  • Solution 2:
    1. Prepare the data using the tidyverse packages. Collapses the two variables ‘psavert’ and ‘uempmed’ into key-value pairs
    2. Visualize using one geom_line() call
# Data preparation
library("tidyverse")
df <- economics %>%
  select(date, psavert, uempmed) %>%
  gather(key = "variable", value = "value", -date)
head(df)
## # A tibble: 6 x 3
##   date       variable value
##   <date>     <chr>    <dbl>
## 1 1967-07-01 psavert   12.5
## 2 1967-08-01 psavert   12.5
## 3 1967-09-01 psavert   11.7
## 4 1967-10-01 psavert   12.5
## 5 1967-11-01 psavert   12.5
## 6 1967-12-01 psavert   12.1
# Visualization
ggplot(df, aes(x = date, y = value)) + 
  geom_line(aes(color = variable, linetype = variable)) + 
  scale_color_manual(values = c("darkred", "steelblue"))



 
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Comments ( 16 )

  • Scot
    22 Aug 2019

    How can you change the size(thickness) of one of the lines in the tidyverse version?

    Reply
    • Kassambara
      22 Aug 2019

      You can specify, for example, the argument size = 3 in the function geom_line()

      Reply
  • Abdi Dahir
    10 Feb 2020

    I have used the first method but i have difficulties with the legend. As you can see, there is no legend indicating the column each line represents. How can i add legend for the first case (method)?

    Reply
    • Eric Reynaud
      02 Mar 2020

      First, you need to set the colors of each line inside aes(…). That will create the legend, but the colors wont be the expected ones . To get them, add
      + scale_color_identity(guide = legend())
      at the end of ggplot() block code

      Reply
      • QB
        26 Apr 2021

        This doesnt work. Argument legend is missing.

        Reply
  • Rasin
    08 Apr 2020

    Thank you Sir
    it is very simple and explained very well

    Reply
  • Keiran
    18 May 2020

    If i want to add more than 2 lines what should i do, i am trying with the second method and it works fine with only 2 but won’t show others

    Reply
    • Kassambara
      18 May 2020

      Hi, please make sure you have specified as many colors as the number of lines. This works for me:

      library("tidyverse")
df <- economics %>%
  select(date, psavert, uempmed) %>%
  mutate(uempmed_2 = 2*uempmed) %>%
  gather(key = "variable", value = "value", -date)

ggplot(df, aes(x = date, y = value)) + 
  geom_line(aes(color = variable, linetype = variable)) + 
  scale_color_manual(values = c("darkred", "steelblue", "green"))

      Reply
  • Rmann
    23 May 2020

    Thank you for this it is very well explained.
    I have following question. In the solution 1 there is no legend for the lines whereas the solution 2 has a legend.
    I was wondering if you can show how to put a legend and chart title etc in Solution 1.
    Thanks

    Reply
    • Kassambara
      23 May 2020

      Thank you for the positive comment, highly appreciated! Here’s how I’ll add a legend: I specify the variable color in aes() and give it the name I want to be displayed in the legend.

      library(ggplot2)
theme_set(theme_minimal())
data(economics)
ggplot(economics, aes(x = date)) +
  geom_line(aes(y = psavert, color = "psavert")) +
  geom_line(aes(y = uempmed, color = "uempmed"), linetype = "twodash") +
  scale_color_manual(values = c("darkred", "steelblue"))

      Reply
      • Rmann
        23 May 2020

        Thank you very much for the quick response. I am a beginner and trying to explore R. I am glad I learned this otherwise it would have been very demotivating.
        Thanks a ton

        Reply
  • Rick
    27 May 2020

    Is there a way to display the last value of each line in the plot? I am new to R and have not found any workable solution. Thank you in advance!

    Reply
  • Shannon Pederson
    04 Aug 2020

    This was terrific! I believe I got your both your examples of coding to work because your variables were all continuous. What if your X variable is categorical (e.g. gender)?

    Reply
  • Sam
    20 Oct 2020

    How do you change the name of the legend values? (I.e. psavert, uempmed, etc.)

    Reply
  • Shehzeen
    10 Nov 2020

    if I want to change word color in legend then what can we do as u scale_color_manual is there any option to change the heading of legends

    Reply

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