Ordered factors in R Programming - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is an ordered factor in R?

An ordered factor in R is a categorical variable where the categories have a natural order or ranking, like 'low', 'medium', 'high'. It helps R understand that the levels have a sequence.

beginner

How do you create an ordered factor in R?

Use the factor() function with the argument ordered = TRUE. For example: factor(c('low', 'medium', 'high'), ordered = TRUE, levels = c('low', 'medium', 'high')).

intermediate

Why specify the levels when creating an ordered factor?

Specifying levels sets the order of categories explicitly. Without it, R might order levels alphabetically, which can be wrong for ordered data.

intermediate

What happens if you compare two ordered factors in R?

R compares their order based on the levels. For example, 'low' < 'medium' is TRUE if levels are set as low < medium < high.

intermediate

Can you convert an unordered factor to an ordered factor?

Yes, by using factor() again with ordered = TRUE and specifying the correct levels order.

Which argument makes a factor ordered in R?

A ordered = TRUE

B levels = TRUE

C order = TRUE

D rank = TRUE

The argument ordered = TRUE tells R to treat the factor as ordered.

What is the default order of levels if you don't specify them in a factor?

A Reverse alphabetical order

B Order of appearance

C Random order

D Alphabetical order

By default, R orders factor levels alphabetically unless you specify otherwise.

If f is an ordered factor with levels low < medium < high, what is the result of f[1] < f[2] when f[1] = 'low' and f[2] = 'high'?

A Error

B TRUE

C FALSE

D NA

Since 'low' is less than 'high' in the order, the comparison returns TRUE.

How do you check if a factor is ordered in R?

A Use <code>is.ordered_factor()</code>

B Use <code>is.factor()</code>

C Use <code>is.ordered()</code>

D >edoc/<)(rotcaf_deredro.si>edoc< esU

The function is.ordered() returns TRUE if the factor is ordered.

What happens if you compare unordered factors with < or > in R?

A It returns NA

B It compares alphabetically

C It compares based on levels order

D It gives an error

Comparing unordered factors with < or > returns NA (with a warning) because '<' is not meaningful for factors.

Explain what an ordered factor is and why it is useful in R.

Think about categories like 'small', 'medium', 'large' that have a clear order.

Describe how to create an ordered factor from a character vector in R.

Remember to tell R the order of categories explicitly.