Array unique and flip in PHP - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the PHP function array_unique() do?

It removes duplicate values from an array, keeping only the first occurrence of each value.

beginner

What is the purpose of the PHP function array_flip()?

It swaps the keys and values of an array, turning values into keys and keys into values.

beginner

Given $arr = ['apple', 'banana', 'apple', 'orange'];, what is the result of array_unique($arr);?

The result is ['apple', 'banana', 'orange'] with keys preserved as [0 => 'apple', 1 => 'banana', 3 => 'orange'].

intermediate

What happens if you use array_flip() on an array with duplicate values?

Only the last key for each value is preserved because keys must be unique. Earlier keys are overwritten.

intermediate

How can you combine array_unique() and array_flip() to get a flipped array with unique values as keys?

First use array_unique() to remove duplicates, then use array_flip() to swap keys and values, ensuring keys are unique.

What does array_unique() return when given an array with duplicate values?

A An array sorted in ascending order

B An array with duplicates removed, preserving the last occurrence keys

C An array with all values replaced by keys

D An array with duplicates removed, preserving the first occurrence keys

array_unique() removes duplicates and keeps the first occurrence's key.

What will array_flip(['a' => 1, 'b' => 2, 'c' => 1]) return?

A Array with keys and values swapped, last duplicate key kept

B Array with keys and values swapped, first duplicate key kept

C Original array unchanged

D Error because of duplicate values

When flipping, duplicate values become keys; only the last key is kept.

Which function would you use to remove duplicate values from an array in PHP?

A array_flip()

B array_unique()

C array_merge()

D array_slice()

array_unique() removes duplicate values.

If you want to swap keys and values of an array, which function do you use?

A array_unique()

B array_keys()

C array_flip()

D array_reverse()

array_flip() swaps keys and values.

What is a potential problem when using array_flip() on an array with non-unique values?

A It keeps only the last key for duplicate values

B It duplicates keys

C It causes a syntax error

D It sorts the array

Duplicate values become keys, but keys must be unique, so only the last key remains.

Explain how array_unique() and array_flip() work and how they can be used together.

Think about removing duplicates first, then swapping keys and values.

What happens if you flip an array with duplicate values? How does PHP handle the keys?

Consider how keys in PHP arrays must be unique.