Knowledge Quiz: Basic Commands

Note

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

y <- 77 <- yy + 7y <- 67 -> y

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

• 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.
• This command adds the value of y to the value of 7 and prints the result.
• That’s the correct assignment operator, but this command assigns the wrong value.
• This is technically valid assignment, but putting the variable on the right-hand side of the assignment operator is not recommended style.

What value will the following R code produce?

(7 - 3) * 4 - 2

By applying the appropriate order of operations, we get 14.

What value will the following R code produce?

2 + 3 * 4

By applying the appropriate order of operations (parentheses before multiplication/division before addition/subtraction), we get 14.

Which of the following expressions will return TRUE?

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

• FALSE: “alice” is not equal to “bob”, and “alice” is equal to “alice”
• TRUE: “alice” is not equal to “bob”, but “alice is equal to”alice”
• FALSE: “foo” is not equal to “bar”
• FALSE: “alice” is not equal to “bob”
• FALSE: 7 is equal to 7, but 7 is not strictly greater than 7
• FALSE: Trivially

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

5 + 5
# 5 - 5
5 * 5

An error, because the second line is invalid R code10, 0, and 2510 and 00 and 2510 and 25

• Incorrect: a # simply marks the rest of the line as a comment; it doesn’t cause an error.
• Incorrect: the commented line is never evaluated by R, so 0 is never printed.
• Incorrect: the third line (5 * 5) is still evaluated and printed.
• Incorrect: the first line (5 + 5) is still evaluated and printed.
• Correct: the line starting with # is a comment and is never evaluated, so R only prints the results of the first and third lines.