select() for column selection in R Programming - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the select() function do in R's dplyr package?

It chooses specific columns from a data frame, making it easy to work only with the data you need.

beginner

How do you select columns name and age from a data frame df using select()?

Use select(df, name, age) to get only those two columns.

intermediate

Can select() use helper functions like starts_with()?

Yes! You can select columns that start with a pattern, for example select(df, starts_with('a')) picks all columns starting with 'a'.

beginner

What happens if you use select() with a column name that does not exist?

You get an error telling you the column is not found, so you need to check column names carefully.

intermediate

How can you deselect a column using select()?

Use a minus sign before the column name, like select(df, -age) to drop the age column.

What does select(df, name, age) do?

A Renames columns 'name' and 'age'

B Deletes columns 'name' and 'age' from df

C Filters rows where name and age are present

D Selects only the columns 'name' and 'age' from df

select() chooses columns, so it keeps only 'name' and 'age' columns from the data frame.

How do you exclude the column 'salary' using select()?

A select(df, salary)

B select(df, -salary)

C select(df, exclude(salary))

D select(df, drop(salary))

Using a minus sign before the column name tells select() to drop that column.

Which helper function selects columns starting with 'temp'?

A contains('temp')

B ends_with('temp')

C starts_with('temp')

D matches('temp')

starts_with() picks columns whose names begin with the given string.

What will happen if you try select(df, unknown_column)?

A Throws an error about missing column

B Returns an empty data frame

C Returns all columns

D Automatically creates the column

select() requires existing columns; unknown columns cause an error.

Which of these is a correct way to select columns 'x' and 'y'?

A select(df, x, y)

B select(df, c('x', 'y'))

C select(df, ['x', 'y'])

D select(df, x & y)

select() takes column names as separate arguments.

Explain how to use select() to pick specific columns from a data frame.

Think about how you tell R which columns you want to keep.

Describe how to exclude columns using select() and how helper functions can help select columns by pattern.

Remember you can both pick and drop columns easily.