This R graphics tutorial describes how to change **line types in R** for plots created using either the R base plotting functions or the ggplot2 package.

In R base plot functions, the options **lty** and **lwd** are used to specify the line type and the line width, respectively. In ggplot2, the parameters **linetype** and **size** are used to decide the type and the size of lines, respectively.

You will learn how to:

**Display**easily the list of**the different types line graphs**present in R.- Plot two lines and
**modify automatically the line style**for base plots and ggplot by groups. **Adjust the R line thickness**by specifying the options lwd (base plot) and size (ggplot2).**Change manually the appearance**(linetype, color and size) of ggplot lines by using, respectively, the function*scale_linetype_manual*(),*scale_color_manual*() and*scale_size_manual*().

Contents:

## Key R functions

`plot(x, y, type = "b", lty = 1, lwd = 1, col = "blue")`

and`lines(x, y, lty = 2, lwd = 1)`

: Base R plot functions to create line plots.`geom_line(aes(x, y), data = NULL, linetype = "dashed", color = "black", size = 1)`

: ggplot2 function to create line plots.`scale_linetype_manual()`

,`scale_color_manual()`

and`scale_size_manual()`

: ggplot2 functions to set manually lines type, color and size.

## Show the different line types in R

The list of line types available in R, includes:

- “blank”, 1. “solid”, 2. “dashed”, 3. “dotted”, 4. “dotdash”, 5. “longdash” and 6. “twodash”.

Note that, to specify line types, you can use either full names or numbers : 0, 1, 2, 3, 4, 5, 6. 0 is for “blank”, 1 is for “solid”, 2 is for “dashed”, and so on

The graph below illustrates the list of line types available in R:

```
library(ggpubr)
show_line_types()
```

In the next sections, we’ll illustrate line type modification using the example of line plots created with the geom_line(). However, note that, the option linetype can be also applied on other ggplot functions, such as: geom_smooth, geom_density, geom_sgment, geom_hline, geom_vline, geom_abline, geom_smooth and more.

## Change R base plot line types

Simple format of R lines functions:

`plot(x, y, type = "l", lty = 1)`

. Create the main R base plot frame.`lines(x, y, type = "l", lty = 1)`

. Add lines onto the plot.

Key options:

`x`

,`y`

: variables to be used for the x and y axes, respectively.`type`

: display the data as line and/or point. Lowed values:`l`

(display line only),`p`

(show point only) and`b`

(show both).`pch`

and`cex`

: set points shape and size, respectively.`lty`

,`lwd`

: set line types and thickness.`col`

: change the color of point and line.`xlab`

and`ylab`

: for x and y axis labels, respectively.

Create a plot with multiple lines and set the legend lty. We start by plotting a first single line with a solid line type (`lty = 1`

). Next, we add a second line with a dashed line style (`lty = 2`

). Finally, we add a legend on the plot using the R base function `legend()`

, which take the same `col`

and `lty`

arguments as the lines function. The option `cex`

is used to set the legend text size.

```
# 1. Create some variables
x <- 1:10
y1 <- x*x
y2 <- 2*y1
# 2. Plot a first line
plot(x, y1, type = "b", frame = FALSE, pch = 19,
col = "red", xlab = "x", ylab = "y",
lty = 1, lwd = 1)
# 3. Add a second line
lines(x, y2, pch = 18, col = "blue", type = "b",
lty = 2, lwd = 1)
# 4. Add a legend to the plot and set legend lty
legend("topleft", legend = c("Line 1", "Line 2"),
col = c("red", "blue"), lty = 1:2, cex = 0.8)
```

## Change ggplot line types

Data set: `ToothGrowth`

```
ToothGrowth$dose <- as.factor(ToothGrowth$dose)
head(ToothGrowth, 3)
```

```
## len supp dose
## 1 4.2 VC 0.5
## 2 11.5 VC 0.5
## 3 7.3 VC 0.5
```

- Basic line plot showing the mean value of tooth length (
`len`

) by the dose of vitamin C (`dose`

):

- Compute the mean of tooth length grouped by dose:

```
library(dplyr)
df <- ToothGrowth %>%
group_by(dose) %>%
summarise(len.mean = mean(len))
df
```

```
## # A tibble: 3 x 2
## dose len.mean
## <fct> <dbl>
## 1 0.5 10.6
## 2 1 19.7
## 3 2 26.1
```

- Create a single line plot. Change the linetype option to “dashed”.

```
library(ggplot2)
ggplot(data = df, aes(x = dose, y = len.mean, group = 1)) +
geom_line(linetype = "dashed")+
geom_point()
```

- Create a line plot for multiple groups. Change line types by groups.

- Data:

```
# Compute the mean of `len` grouped by dose and supp
library(dplyr)
df2 <- ToothGrowth %>%
group_by(dose, supp) %>%
summarise(len.mean = mean(len))
df2
```

```
## # A tibble: 6 x 3
## # Groups: dose [?]
## dose supp len.mean
## <fct> <fct> <dbl>
## 1 0.5 OJ 13.2
## 2 0.5 VC 7.98
## 3 1 OJ 22.7
## 4 1 VC 16.8
## 5 2 OJ 26.1
## 6 2 VC 26.1
```

- Line plot:

```
# Change line types by groups
ggplot(df2, aes(x = dose, y = len.mean, group = supp)) +
geom_line(aes(linetype = supp))+
geom_point()+
theme(legend.position = "top")
# Change line types + colors by groups
ggplot(df2, aes(x = dose, y = len.mean, group = supp)) +
geom_line(aes(linetype = supp, color = supp))+
geom_point(aes(color = supp))+
theme(legend.position = "top")
```

- Change the appearance of line types manually:

*scale_linetype_manual*(): change line types*scale_color_manual*(): change line colors*scale_size_manual*(): change the size of lines

To be able to apply these functions, you should create a geom_line, which line types, color and size should be controlled by groups.

```
# Change manually line type and color manually
ggplot(df2, aes(x = dose, y = len.mean, group = supp)) +
geom_line(aes(linetype = supp, color = supp))+
geom_point(aes(color = supp))+
scale_linetype_manual(values=c("solid", "dashed"))+
scale_color_manual(values=c("#00AFBB","#FC4E07"))
```

## Conclusion

- Use
**lty**and**lwd**options, for changing lines type and thickness in R base graphics:

```
x <- 1:10; y1 <- x*x; y2 <- 2*y1
# Draw two lines
plot(x, y1, type = "b", pch = 19, col = "red", lty = 1, lwd = 1)
lines(x, y2, pch = 18, col = "blue", type = "b", lty = 2, lwd = 1)
# Add legend
legend("topleft", legend = c("Line 1", "Line 2"),
col = c("red", "blue"), lty = 1:2)
```

- Use
**linetype**and**size**arguments in ggplot2 :

```
# Create some data
x <- 1:10; y1 <- x*x; y2 <- 2*y1
df <- data.frame(
x = c(x, x), y = c(y1, y2),
grp = as.factor(rep(c("A", "B"), each = 10))
)
# Plot
library(ggplot2)
ggplot(data = df, aes(x, y, group = grp)) +
geom_line(aes(linetype = grp))+
geom_point()
```

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