Line graph with multiple lines in ggplot2

Data transformation

Consider the following data frame where each column represents the path of a brownian motion.

# Brownian motion
set.seed(2)

# Grid
t <- seq(0, 1, by = 0.001)
p <- length(t) - 1

# 5 paths
n <- 5
I <- matrix(rnorm(n * p, 0, 1 / sqrt(p)), n, p)

# Data frame
df1 <- data.frame(apply(I, 1, cumsum))

In order to use your data frame in ggplot2 you will need to transform it into long format. You can achieve it making use of the melt function of the reshape package.

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

df <- data.frame(x = seq_along(df1[, 1]),
                 df1)

# Long format
df <- melt(df, id.vars = "x")

Line chart of several variables

Given a data frame in long format like df it is possible to create a line chart with multiple lines in ggplot2 with geom_line the following way.

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

ggplot(df, aes(x = x, y = value, color = variable)) +
  geom_line()

Line graph of multiple lines in ggplot2

Lines width and style

The styling of the lines can be changed making use of the arguments of geom_line, like linetype for changing the style of the line or lwd to change its width.

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

ggplot(df, aes(x = x, y = value, color = variable)) +
  geom_line(linetype = 3,
            lwd = 1.1)

Line chart customization in ggplot2

Color customization

The default color palette can be changed passing a vector of colors to the values argument of the scale_color_manual function.

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

# Color selection
cols <- c("#D43F3A", "#EEA236", "#5CB85C", "#46B8DA", "#9632B8")

ggplot(df, aes(x = x, y = value, color = variable)) +
  geom_line() +
  scale_color_manual(values = cols)

Change the color of a line chart by group in ggplot2

Highlight some lines

Note that using the previous method you can also highlight some lines of the chart, using the same color for all lines but some.

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

# Color selection
cols <- c("gray", "gray", "gray", "#5CB85C", "gray")

ggplot(df, aes(x = x, y = value, color = variable)) +
  geom_line() +
  scale_color_manual(values = cols)

Highlight line in ggplot2

Legend customization

Change the title of the legend of a line chart in ggplot2

Title

You can change the default title for the legend of the line chart with guide_legend as shown below.

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

ggplot(df, aes(x = x, y = value, color = variable)) +
  geom_line() +
  guides(color = guide_legend(title = "Title"))

Change the key legend labels of a ggplot2 line chart

Legend labels

The labels of the legend can be modified making use of the labels argument of scale_color_discrete.

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

ggplot(df, aes(x = x, y = value, color = variable)) +
  geom_line() +
  scale_color_discrete(labels = paste("V", 1:5))

Remove the legend of a line graph in ggplot2

Remove the legend

You can also get rid of the legend making use of legend.position = "none".

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

ggplot(df, aes(x = x, y = value, color = variable)) +
  geom_line() +
  theme(legend.position = "none")