Knowledge Quiz: Basic Commands

Which of the following commands represents the recommended way to assign the value 7 to the object y?

y <- 6y < 7y = 7y <- 77 <- y

Although there are three valid assignment operators: <-, ->, =, only the left-facing arrow is recommended by most style guides.

• That’s the correct assignment operator, but this command assigns the wrong value.
• This is a logical comparison. We’re checking if the value of y is less than 7.
• While = is a legal assignment operator, using an equals sign for assignment is not recommended style.
• Correct
• This isn’t legal R code. This command attempts to assign the value y to the variable 7, but variable names can’t begin with numbers.

What value will the following R code produce?

10 - 2 * 3

By applying the appropriate order of operations (parentheses before multiplication/division before addition/subtraction), we get 4.

Which of the following expressions will return TRUE?

(8 - 1) == 7 & 7 > (14 / 2)FALSE"alice" == "bob" | "alice" == "alice""alice" == "bob" | "alice" != "alice""foo" == "bar"

• FALSE: 7 is equal to 7, but 7 is not strictly greater than 7 (both conditions must be true)
• FALSE: Trivially
• TRUE: “alice” is not equal to “bob”, but “alice is equal to”alice” (at least one condition must be true)
• FALSE: “alice” is equal to “alice”, but “alice” is not equal to “bob” (both conditions must be true)
• FALSE: “foo” is not equal to “bar”

What will the following R code print when you run it?

# 4 * 2
# 4 - 2
4 / 2
4^2

An error, because the first two lines are not valid R code2 and 168, 2, 2, and 1620, 0, 2, and 16

• A # character simply marks the rest of the line as a comment. These comments would not cause an error.
• The lines starting with # are comment and are never evaluated, so R only prints the results of the last two lines.
• Commented lines are not evaluated as R code, so no output would be printed for the first two lines.
• Both the third and fourth lines are evaluated, so we would see two printed values.
• Commented lines are not evaluated as R code, so no 0 would be printed.

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