Line graph in ggplot2 [geom_line and geom_step]

Basic line charts with geom_line
Stairstep plots with geom_step
Line colors and styles

Basic line charts with `geom_line`

Given a data frame with a numerical variable x and a numerical variable y representing the value for each observation it is possible to create a line chart in ggplot with geom_line as follows.

# install.packages("ggplot2")
library(ggplot2)

# Data
set.seed(1)
x <- 1:20
y <- x ^ 2 + runif(20, 0, 100)
df <- data.frame(x = x, y = y)

ggplot(df, aes(x = x, y = y)) +
  geom_line()

Basic line graph in ggplot2

Adding points

If you add geom_point to the plot a point will be added for each observation.

# install.packages("ggplot2")
library(ggplot2)

# Data
set.seed(1)
x <- 1:20
y <- x ^ 2 + runif(20, 0, 100)
df <- data.frame(x = x, y = y)

ggplot(df, aes(x = x, y = y)) +
  geom_line() +
  geom_point()

Line chart with points in ggplot2

Line as an arrow

If your data represents a trend or a path you can end the line with an arrow, passing the arrow funtion to the arrow argument. Type ?arrow for additional arguments.

# install.packages("ggplot2")
library(ggplot2)

# Data
set.seed(1)
x <- 1:20
y <- x ^ 2 + runif(20, 0, 100)
df <- data.frame(x = x, y = y)

ggplot(df, aes(x = x, y = y)) +
  geom_line(arrow = arrow())

Stairstep plots with `geom_step`

Stairs plot in ggplot2

First horizontal

An alternative geom is geom_step, which will create a stairstep plot where the first line is horizontal by default.

# install.packages("ggplot2")
library(ggplot2)

# Data
set.seed(1)
x <- 1:20
y <- x ^ 2 + runif(20, 0, 100)
df <- data.frame(x = x, y = y)

ggplot(df, aes(x = x, y = y)) +
  geom_step()

Stair step graph in ggplot2

First vertical

To set the first line vertical pass the string "vh" to the direction argument of the geom.

# install.packages("ggplot2")
library(ggplot2)

# Data
set.seed(1)
x <- 1:20
y <- x ^ 2 + runif(20, 0, 100)
df <- data.frame(x = x, y = y)

ggplot(df, aes(x = x, y = y)) +
  geom_step(direction = "vh")

Using the geom_step function

Step half-way between values

Other possible option is setting "mid", for step half-way between adjacent X-axis values.

# install.packages("ggplot2")
library(ggplot2)

# Data
set.seed(1)
x <- 1:20
y <- x ^ 2 + runif(20, 0, 100)
df <- data.frame(x = x, y = y)

ggplot(df, aes(x = x, y = y)) +
  geom_step(direction = "mid")

Line colors and styles

The color, lwd and linetype arguments can be used to modify the color, width and the type of the lines, respectively.

# install.packages("ggplot2")
library(ggplot2)

# Data
set.seed(1)
x <- 1:20
y <- x ^ 2 + runif(20, 0, 100)
df <- data.frame(x = x, y = y)

ggplot(df, aes(x = x, y = y)) +
  geom_line(color = 4,    # Color of the line
            lwd = 1,      # Width of the line
            linetype = 1) # Line type

Line chart in ggplot color and style customization

Note that the line type can be set with numbers (0 to 6), with texts or with string patterns.

# install.packages("ggplot2")
library(ggplot2)

# Data
set.seed(1)
x <- 1:20
y <- x ^ 2 + runif(20, 0, 100)
df <- data.frame(x = x, y = y)

ggplot(df, aes(x = x, y = y)) +
  geom_line(color = 4,
            lwd = 1,  
            linetype = "dashed")