Modifying and adding elements in R Programming - Cheat Sheet & Quick Revision

Recall & Review

beginner

How do you change the value of an element in a vector in R?

You assign a new value to the element using its index. For example, vec[2] <- 10 changes the second element to 10.

beginner

What function can you use to add elements to the end of a vector?

You can use the c() function to combine vectors or add elements. For example, vec <- c(vec, 5) adds 5 to the end.

beginner

How do you add a new column to a data frame in R?

Assign a vector to a new column name. For example, df$new_col <- c(1,2,3) adds a column named 'new_col'.

intermediate

How can you modify an element inside a list in R?

Use double brackets with the element name or index. For example, mylist[["item"]] <- 42 changes the 'item' element.

intermediate

What happens if you assign a value to an index outside the current length of a vector?

R extends the vector and fills missing elements with NA. For example, vec[5] <- 10 makes elements 3 and 4 NA if they didn't exist.

Which syntax correctly adds a new element 7 to the end of vector v?

A v <- c(v, 7)

B v[7] <- v

C v + 7

D append(v, 7)

Use c() to combine vectors or add elements. v <- c(v, 7) adds 7 at the end.

How do you change the third element of vector x to 100?

A x(3) = 100

B x[3] <- 100

C x <- 100[3]

D x[[3]] <- 100

Use single brackets with index to modify vector elements: x[3] <- 100.

Which is the correct way to add a new column named 'age' to data frame df?

A df <- c(df, age)

B df[age] <- c(25, 30, 35)

C df(age) <- c(25, 30, 35)

D df$age <- c(25, 30, 35)

Use $ to add a new column: df$age <- c(25, 30, 35).

What happens if you assign a value to vec[10] when vec has length 5?

A Vector extends; elements 6 to 9 become NA

B Error: index out of bounds

C Nothing changes

D Vector shrinks to length 10

R extends the vector and fills missing elements with NA.

How do you modify the element named 'score' in a list lst?

A lst[score] <- new_value

B lst.score <- new_value

C lst[['score']] <- new_value

D lst(score) <- new_value

Use double brackets with the element name: lst[['score']] <- new_value.

Explain how to modify an element in a vector and add a new element at the end in R.

Think about using brackets for modification and c() for adding.

Describe how to add a new column to a data frame and how to modify an element inside a list.

Remember data frames and lists have different ways to access elements.