This article describes the different **pch in R** for modifying the point symbols of an R base plot. The option `pch`

is used to specify point symbols in the functions `plot()`

and `lines()`

.

In this tutorial, you’ll learn how to:

**Display easily the list of pch in R**. The R function`ggpubr::show_point_shapes()`

can be used to show the 25 commonly used R pch values.**Change the R base plot pch symbols and appearance**. Additionally, we provide R codes to modify the plot**pch size**and**pch color**, as well as, the**legend pch**. key arguments in`plot()`

function:`pch`

: numeric values (from 0 to 25) or character symbols (“+”, “.”, “;”, etc) specifying the point symbols (or shapes).`cex`

: numeric values indicating the point size.`col`

: color name for points.

**Control pch types by groups**.**Use special pch types, including pch 21 and pch 24**. The interesting feature of these pch codes is that you can change their background fill color and, their border line type and color.

Contents:

## Key R functions

`plot(x, y, pch = 19, col = "black", cex = 1)`

: Base R plot function to create a scatter plot.

## List of pch symbols

The most commonly used pch values in R, include:

- pch = 0, square
- pch = 1, circle
- pch = 2, triangle point up
- pch = 3, plus
- pch = 4, cross
- pch = 5, diamond
- pch = 6, triangle point down
- pch = 7, square cross
- pch = 8, star
- pch = 9, diamond plus
- pch = 10, circle plus
- pch = 11, triangles up and down
- pch = 12, square plus
- pch = 13, circle cross
- pch = 14, square and triangle down
- pch = 15, filled square
- pch = 16, filled circle
- pch = 17, filled triangle point-up
- pch = 18, filled diamond
- pch = 19, solid circle
- pch = 20, bullet (smaller circle)
- pch = 21, filled circle blue
- pch = 22, filled square blue
- pch = 23, filled diamond blue
- pch = 24, filled triangle point-up blue
- pch = 25, filled triangle point down blue

The function below illustrates the different pch values. First install the `ggpubr`

package (`install.packages("ggpubr")`

), and then type this:

`ggpubr::show_point_shapes()`

Note that,

- points can be omitted from the plot using pch = NA.
- Other different characters symbols can be used to specify the pch argument, including “+”, “*“,”-“,”.“,”#, “%”, “o”.
- pch options from pch 21 to 25 are open symbols that can be filled by a color.

## Demo dataset

We’ll use the R built-in datasets: `iris`

.

`head(iris, 3)`

```
## Sepal.Length Sepal.Width Petal.Length Petal.Width Species
## 1 5.1 3.5 1.4 0.2 setosa
## 2 4.9 3.0 1.4 0.2 setosa
## 3 4.7 3.2 1.3 0.2 setosa
```

## Change R base plot point shapes

The default R plot `pch`

symbol is 1, which is an empty circle. You can change this to `pch = 19`

(solid circle) or to `pch = 21`

(filled circle).

For example:

```
# Default plot pch = 1 (empty circle)
plot(x = iris$Sepal.Length, y = iris$Sepal.Width, frame = FALSE,
xlab = "Sepal Length", ylab = "Sepal Width")
# Change plot symbol to pch = 19 (solid circle)
plot(x = iris$Sepal.Length, y = iris$Sepal.Width, frame = FALSE,
xlab = "Sepal Length", ylab = "Sepal Width",
pch = 19)
```

To change the color and the size of points, use the following arguments:

`col`

: color (hexadecimal color code or color name). For example,`col = "blue"`

or`col = "#4F6228"`

.`cex`

: the size of point symbols. Numeric values.

For the filled pch symbols (21 to 25), you can use additional plot options to modify the points background color (`bg`

) and the border line width (`lwd`

):

`bg`

: the background (or fill) color for the open plot symbols (21 to 25).`lwd`

: Numeric values indicating the line width of the plotting symbols border.

```
# Change color
plot(x = iris$Sepal.Length, y = iris$Sepal.Width, frame = FALSE,
xlab = "Sepal Length", ylab = "Sepal Width",
pch = 19, col = "#0073C2FF")
# Use pch = 21
# Change border line width (lwd), and background color (bg)
plot(x = iris$Sepal.Length, y = iris$Sepal.Width, frame = FALSE,
xlab = "Sepal Length", ylab = "Sepal Width",
pch = 21, bg = "lightgray", col = "black",
lwd = 0.9, cex = 1.5)
```

Note that point color and pch can be also a vector. For example, you might want to change point colors and shapes by groups:

```
# Define color for each of the 3 iris species
colors <- c("#00AFBB", "#E7B800", "#FC4E07")
colors <- colors[as.numeric(iris$Species)]
# Define shapes
shapes = c(16, 17, 18)
shapes <- shapes[as.numeric(iris$Species)]
# Plot
plot(x = iris$Sepal.Length, y = iris$Sepal.Width, frame = FALSE,
xlab = "Sepal Length", ylab = "Sepal Width",
col = colors, pch = shapes)
legend("topright", legend = levels(iris$Species),
col = c("#00AFBB", "#E7B800", "#FC4E07"),
pch = c(16, 17, 18) )
```

## Conclusion

This article describes the different point shapes (or pch symbols) available in R.

- Display the different point symbols in R:

`ggpubr::show_point_shapes()`

- Change point symbols in R base plots. Use
**pch**,**cex**and**col**to change, respectively, the symbols, the size and the color of points in R base plots:

```
plot(x = iris$Sepal.Length, y = iris$Sepal.Width, frame = FALSE,
xlab = "Sepal Length", ylab = "Sepal Width",
pch = 19, cex = 1, col = "#00AFBB")
```

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Version: Français

If you want to convert a string to numeric, it´s better to use as.factor, instead of as.numeric

Thank you for your input. Note that the variable “iris$Species” is already a factor