select() for column selection in R Programming - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of select() with tidyselect helpers

What is the output of the following R code using dplyr::select() with tidyselect helpers?

R Programming

library(dplyr)
df <- tibble(a = 1:3, b = 4:6, c = 7:9, d = 10:12)
result <- df %>% select(starts_with("b"), ends_with("d"))
print(result)

A A tibble with columns a, b, c, d

B A tibble with columns a and c

C A tibble with columns b and d

D An error because ends_with() is used incorrectly

💡 Hint

Think about which columns start with 'b' and which end with 'd'.

The select() function picks columns starting with 'b' (which is 'b') and ending with 'd' (which is 'd'). So the result has columns 'b' and 'd'.

❓ Predict Output

intermediate

Result of select() with numeric range

What columns are selected by this code snippet?

R Programming

library(dplyr)
df <- tibble(x1 = 1:2, x2 = 3:4, y1 = 5:6, y2 = 7:8)
selected <- df %>% select(x1:y1)
print(selected)

A Columns x1, x2, y1, y2

B Columns x1, x2, y1

C Columns x1 and y1 only

D Error because x1:y1 is invalid

💡 Hint

The colon operator selects columns between two names in order.

The select(x1:y1) picks columns from x1 through y1 in the order they appear: x1, x2, y1.

🔧 Debug

advanced

Why does this select() call fail?

This code throws an error. What is the cause?

R Programming

library(dplyr)
df <- tibble(a = 1:3, b = 4:6)
selected <- df %>% select(a, c)
print(selected)

A Column 'c' does not exist in the data frame

B select() cannot take multiple arguments

C The pipe operator %>% is used incorrectly

D The tibble function is missing parentheses

💡 Hint

Check if all columns you select exist in the data frame.

The error occurs because column 'c' is not present in df, so select() cannot find it.

❓ Predict Output

advanced

Output of select() with helper functions and renaming

What is the output of this code?

R Programming

library(dplyr)
df <- tibble(name = c("Ann", "Bob"), age = c(25, 30), score = c(88, 92))
result <- df %>% select(person = name, age)
print(result)

A A tibble with columns 'age' and 'score' only

B A tibble with columns 'name' and 'age' unchanged

C An error because select() cannot rename columns

D A tibble with columns 'person' and 'age', where 'person' has the names

💡 Hint

select() can rename columns by using new_name = old_name syntax.

The select() call renames 'name' to 'person' and keeps 'age'. So the output has columns 'person' and 'age'.

🧠 Conceptual

expert

Understanding select() with complex tidyselect expressions

Which option correctly describes the columns selected by this code?

R Programming

library(dplyr)
df <- tibble(a1 = 1, a2 = 2, b1 = 3, b2 = 4, c1 = 5)
selected <- df %>% select(matches("^a[12]$"), -a2)
print(selected)

A Only column 'a1' is selected because 'a2' is excluded

B An error occurs because negative selection cannot be combined with matches()

C Columns 'a1', 'a2', and 'b1' are selected

D Columns 'a1' and 'a2' are selected because matches() includes both

💡 Hint

Negative selection removes columns after positive selection.

matches("^a[12]$") selects 'a1' and 'a2'. Then '-a2' removes 'a2', leaving only 'a1'.