Saving plots (ggsave) in R Programming - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output file type saved by this ggsave command?

Consider the following R code that creates a plot and saves it using ggsave. What file type will be created?

R Programming

library(ggplot2)
p <- ggplot(mtcars, aes(x=wt, y=mpg)) + geom_point()
ggsave(filename = "myplot.png", plot = p)

A A PDF file named 'myplot.png' is saved

B A PNG file named 'myplot.png' is saved

C A JPEG file named 'myplot.png' is saved

D No file is saved because the extension is incorrect

💡 Hint

Check the file extension in the filename argument.

ggsave uses the file extension to determine the output format. Since the filename ends with '.png', it saves a PNG file.

❓ Predict Output

intermediate

What will be the dimensions of the saved plot?

What are the width and height in inches of the saved plot from this code?

R Programming

library(ggplot2)
p <- ggplot(mtcars, aes(x=wt, y=mpg)) + geom_point()
ggsave(filename = "plot.pdf", plot = p, width = 5, height = 4)

A Width 5 inches, Height 4 inches

B Width 4 inches, Height 5 inches

C Width and height default to 7 inches each

D Width and height are ignored and plot size depends on screen size

💡 Hint

Look at the width and height arguments in ggsave.

The width and height arguments set the size of the saved plot in inches. Here, width=5 and height=4 inches.

❓ Predict Output

advanced

What error does this ggsave command produce?

What error will this code produce when run?

R Programming

library(ggplot2)
p <- ggplot(mtcars, aes(x=wt, y=mpg)) + geom_point()
ggsave(filename = "plot", plot = p)

A Error: Unknown graphics device 'plot'

B No error, saves a file named 'plot' with default format

C Error: No file extension provided in filename

D Error: plot object is missing

💡 Hint

ggsave needs a file extension to know the format.

ggsave requires a file extension to determine the output format. Without it, it throws an error about missing extension.

❓ Predict Output

advanced

What is the resolution (dpi) of the saved image?

What is the dpi (dots per inch) of the saved plot from this code?

R Programming

library(ggplot2)
p <- ggplot(mtcars, aes(x=wt, y=mpg)) + geom_point()
ggsave(filename = "plot.png", plot = p, dpi = 300)

A 300 dpi

B 150 dpi

C 72 dpi

D Default dpi depends on device and is not set here

💡 Hint

Check the dpi argument in ggsave.

The dpi argument sets the resolution of the saved image. Here it is explicitly set to 300 dpi.

❓ Predict Output

expert

What is the output of this code saving multiple plots in a loop?

What files will be created and what will be their contents after running this code?

R Programming

library(ggplot2)
for(i in 1:3) {
  p <- ggplot(mtcars, aes(x=wt, y=mpg)) + geom_point() + ggtitle(paste("Plot", i))
  ggsave(filename = paste0("plot", i, ".png"), plot = p, width = 4, height = 3)
}

A No files are saved because ggsave cannot be used inside a loop

B One PNG file named plot3.png with the last plot titled 'Plot 3'

C Three PNG files named plot1.png, plot2.png, plot3.png but all plots have the title 'Plot 3'

D Three PNG files named plot1.png, plot2.png, plot3.png each with a scatter plot titled 'Plot 1', 'Plot 2', and 'Plot 3' respectively

💡 Hint

Look at the filename and title inside the loop.

The loop creates three separate plots with different titles and saves each to a uniquely named file.