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Exercise

Adjusting text position, size, and font

The previous exercise added explanatory text to a scatterplot. The purpose of this exercise is to improve this plot by modifying the text placement, increasing the text size, and displaying the text in boldface.

It was noted that the adj argument to the text() function determines the horizontal placement of the text and it can take any value between 0 and 1. In fact, this argument can take values outside this range. That is, making this value negative causes the text to start to the right of the specified x position. Similarly, making adj greater than 1 causes the text to end to the left of the x position.

Another useful optional argument for the text() function is cex, which scales the default text size. As a specific example, setting cex = 1.5 increases the text size by 50 percent, relative to the default value. Similarly, specifying cex = 0.8 reduces the text size by 20 percent.

Finally, the third optional parameter used here is font, which can be used to specify one of four text fonts: font = 1 is the default text font (neither italic nor bold), font = 2 specifies bold face text, font = 3 specifies italic text, and font = 4 specifies both bold and italic text.

Instructions
100 XP
  • Create a plot of MPG.city vs. Horsepower from the Cars93 data frame, with data represented as open circles (default pch).
  • Construct the variable index3 using the which() function that identifies the row numbers containing all 3-cylinder cars.
  • Use the points() function to overlay solid circles, pch = 16, on top of all points in the plot that represent 3-cylinder cars.
  • Use the text() function with the Make variable as before to add labels to the right of the 3-cylinder cars, but now use adj = -0.2 to move the labels further to the right, use the cex argument to increase the label size by 20 percent, and use the font argument to make the labels bold italic.