Sorting with order() in R Programming - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the order() function do in R?

The order() function returns the indices that would sort a vector or data frame. You can use these indices to rearrange data in ascending or descending order.

beginner

How do you sort a vector ascending using order()?

Use vec[order(vec)]. This returns the vector elements sorted from smallest to largest.

intermediate

How can you sort a data frame by multiple columns using order()?

Use df[order(df$col1, df$col2), ]. This sorts first by col1, then by col2 within ties.

intermediate

How do you sort in descending order with order()?

Use order(-vec) for numeric vectors. For characters, use order(vec, decreasing = TRUE).

intermediate

Why use order() instead of sort()?

order() gives the positions to rearrange data, useful for sorting data frames or multiple vectors together. sort() just returns a sorted vector.

What does order(c(3,1,2)) return?

A [2, 1, 3]

B [2, 3, 1]

C [3, 1, 2]

D [1, 2, 3]

The order function returns indices that sort the vector. The smallest element is at position 2 (value 1), then position 3 (value 2), then position 1 (value 3).

How do you sort a data frame df by column age ascending?

A df[order(df$age), ]

B order(df$age)

C sort(df$age)

D df[sort(df$age), ]

You use order to get the sorting indices and then reorder the rows of df accordingly.

Which code sorts a vector v in descending order?

A v[order(v)]

B sort(v)

C v[order(-v)]

D order(v, decreasing=TRUE)

Using negative values with order sorts numeric vectors in descending order.

What is the main difference between sort() and order()?

A sort returns sorted values; order returns sorting indices

B order returns sorted values; sort returns indices

C Both return sorted values

D Both return sorting indices

sort() returns the sorted vector, while order() returns the positions to sort the vector.

How do you sort a data frame by two columns, name then score?

A sort(df$name, df$score)

B df[order(df$score, df$name), ]

C order(df$name, df$score)

D df[order(df$name, df$score), ]

You pass multiple columns to order to sort by the first, then the second within ties.

Explain how the order() function works and how it differs from sort().

Think about what you get back from each function and how you use it.

Describe how to sort a data frame by multiple columns using order().

Remember how to handle ties in sorting.