Understanding Function Errors and Saving Plots in R

In this article, we’ll delve into a specific error that occurs when trying to save two plots using an R function. We’ll explore what causes this issue, how to fix it, and provide additional insights into saving plots and working with the graphics device in R.

Introduction to R Graphics Devices

Before we dive into the code, let’s briefly discuss R graphics devices. In R, a graphics device is a virtual representation of where your plot will be displayed. By default, when you call dev.plot(), R uses the “X11” graphics device, which is a window-based interface.

To create a standalone file (like an image) instead of displaying it directly in RStudio or another application, we need to use a different graphics device, such as PNG. The function dev.copy() allows us to copy the current graphics device to a new one, while dev.set(), dev.copy(), and dev.switch() allow us to switch between multiple graphics devices.

Creating Two Plots with R

The provided code snippet demonstrates how to create two plots using the hist() and plot(density()) functions. The issue arises from incorrectly closing the graphics device, leading to an error message indicating that it cannot shut down device 1 (the null device).

Here’s the problematic code:

f1 <- function(x){
  write.table(as.matrix(summary(x)), file="dane.txt", sep=";", row.names=T)
  
  # I want here to make two plots.
  png(filename="hist.png")
  hist(x)
  dev.off()
  
  dev.cur()
  png(filename="density.png")
  plot(density(x))
  dev.off()
}

The Error and Its Solution

The error is caused by the missing closing parenthesis () in the last call to dev.off(). This function indicates that R cannot shut down device 1 because it was already closed.

To fix this, we need to add the required parentheses to properly close both graphics devices:

f1 <- function(x){
  write.table(as.matrix(summary(x)), file="dane.txt", sep=";", row.names=T)
  
  # I want here to make two plots.
  png(filename="hist.png")
  hist(x)
  dev.off()
  
  dev.cur()
  png(filename="density.png")
  plot(density(x))
  dev.off() # Add the closing parenthesis
}

Additional Insights and Considerations

Saving Plots as Images

In R, you can save plots directly as images using various file formats like PNG, JPEG, or PDF. To do this, use the png() function to specify the filename and format.

Here’s an example:

f1 <- function(x){
  write.table(as.matrix(summary(x)), file="dane.txt", sep=";", row.names=T)
  
  # I want here to make two plots.
  png(filename = "hist.png", width = 800, height = 600)
  hist(x)
  dev.off()
  
  dev.cur()
  png(filename = "density.png", width = 800, height = 600)
  plot(density(x))
  dev.off()
}

This code will save both plots as PNG files with specified dimensions.

Working with Multiple Graphics Devices

R allows you to work with multiple graphics devices using the dev.copy() and dev.set() functions. These functions enable you to switch between different graphics devices or copy the current device to a new one.

Here’s an example of switching between two graphics devices:

f1 <- function(x){
  write.table(as.matrix(summary(x)), file="dane.txt", sep=";", row.names=T)
  
  # I want here to make two plots.
  dev.set("png")  # Switch to the PNG device
  
  png(filename = "hist.png")
  hist(x)
  dev.off()
  
  dev.cur()  # Switch back to the default device
  plot(density(x))
}

In this example, we first switch to the PNG graphics device using dev.set("png"). Then, we create a plot and save it as an image. Afterward, we switch back to the default graphics device using dev.cur().

Conclusion

This article demonstrated how to fix an error related to saving plots in R. We explored what causes this issue, how to fix it, and provided additional insights into working with graphics devices in R. Additionally, we discussed creating standalone files (like images) and switching between multiple graphics devices using various functions like dev.copy() and dev.set().

Last modified on 2023-08-05