NULL and NA values in R Programming - Cheat Sheet & Quick Revision

Recall & Review

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What does NULL represent in R?

NULL means no value or an empty object. It shows that something does not exist or is missing completely.

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What is the difference between NA and NULL in R?

NA means a missing value in data, like a blank spot in a table.<br>NULL means no object or no value at all.

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How do you check if a value is NA in R?

Use the function is.na(). It returns TRUE if the value is NA, otherwise FALSE.

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How do you check if an object is NULL in R?

Use the function is.null(). It returns TRUE if the object is NULL, otherwise FALSE.

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What happens if you try to perform arithmetic with NA in R?

The result is usually NA because the missing value affects the calculation.

Which function checks if a value is NA in R?

A is.na()

B is.null()

C is.missing()

D is.empty()

is.na() checks for missing values (NA), while is.null() checks for NULL.

What does NULL mean in R?

A Zero

B A missing value in data

C An empty object or no value

D A string "NULL"

NULL means no object or no value exists.

If you add a number to NA, what is the result?

A An error

B Zero

C The number itself

D <code>NA</code>

Any arithmetic with NA results in NA because the value is missing.

Which function returns TRUE if an object is NULL?

A is.null()

B is.na()

C is.empty()

D is.na.null()

is.null() checks if an object is NULL.

What is the output of length(NULL) in R?

A NULL

B 0

C 1

D NA

NULL has length zero because it means no object.

Explain the difference between NULL and NA in R with examples.

Think about missing data versus no object at all.

How do you test for NA and NULL values in R? Provide the functions and example usage.

Remember the functions start with 'is.'