R Cookbook, 2nd Edition

Chapter 2. Some Basics

The recipes in this chapter lie somewhere between problem-solving ideas and tutorials. Yes, they solve common problems, but the Solutions showcase common techniques and idioms used in most R code, including the code in this cookbook. If you are new to R, we suggest skimming this chapter to acquaint yourself with these idioms.

2.1 Printing Something to the Screen

Problem

You want to display the value of a variable or expression.

Solution

If you simply enter the variable name or expression at the command prompt, R will print its value. Use the print function for generic printing of any object. Use the cat function for producing custom-formatted output.

Discussion

It’s very easy to ask R to print something—just enter it at the command prompt:

pi
#> [1] 3.14
sqrt(2)
#> [1] 1.41

When you enter expressions like these, R evaluates the expression and then implicitly calls the print function. So the previous example is identical to this:

print(pi)
#> [1] 3.14
print(sqrt(2))
#> [1] 1.41

The beauty of print is that it knows how to format any R value for printing, including structured values such as matrices and lists:

print(matrix(c(1, 2, 3, 4), 2, 2))
#>      [,1] [,2]
#> [1,]    1    3
#> [2,]    2    4
print(list("a", "b", "c"))
#> [[1]]
#> [1] "a"
#>
#> [[2]]
#> [1] "b"
#>
#> [[3]]
#> [1] "c"

This is useful because you can always view your data: just print it. You need not write special printing logic, even for complicated data structures.

The print function has a significant ...