Array unique and flip in PHP - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to remove duplicate values from the array.

PHP

<?php
$numbers = [1, 2, 2, 3, 4, 4, 5];
$unique = [1]($numbers);
print_r($unique);
?>

Drag options to blanks, or click blank then click option'

Aarray_unique

Barray_flip

Carray_merge

Darray_map

Attempts:

3 left

💡 Hint

Common Mistakes

Using array_flip instead of array_unique.

Trying to use array_merge which combines arrays.

Using array_map which applies a callback to elements.

The array_unique function removes duplicate values from an array.

2fill in blank

medium

Complete the code to flip keys and values of the array.

PHP

<?php
$colors = ['red', 'green', 'blue'];
$flipped = [1]($colors);
print_r($flipped);
?>

Drag options to blanks, or click blank then click option'

Aarray_reverse

Barray_unique

Carray_flip

Darray_keys

Attempts:

3 left

💡 Hint

Common Mistakes

Using array_unique which removes duplicates.

Using array_reverse which reverses order but not keys and values.

Using array_keys which returns keys only.

The array_flip function swaps the keys and values of an array.

3fill in blank

hard

Fix the error in the code to correctly remove duplicates and flip the array.

PHP

<?php
$items = ['a', 'b', 'a', 'c'];
$unique = [1]($items);
$flipped = array_flip($unique);
print_r($flipped);
?>

Drag options to blanks, or click blank then click option'

Aarray_flip

Barray_unique

Carray_merge

Darray_map

Attempts:

3 left

💡 Hint

Common Mistakes

Using array_flip first which does not remove duplicates.

Using array_merge which combines arrays incorrectly.

Using array_map which is not for removing duplicates.

First remove duplicates with array_unique, then flip keys and values.

4fill in blank

hard

Fill both blanks to create an array of unique values and then flip keys and values.

PHP

<?php
$fruits = ['apple', 'banana', 'apple', 'orange'];
$unique = [1]($fruits);
$flipped = [2]($unique);
print_r($flipped);
?>

Drag options to blanks, or click blank then click option'

Aarray_unique

Barray_flip

Carray_merge

Darray_reverse

Attempts:

3 left

💡 Hint

Common Mistakes

Using array_merge instead of array_unique.

Using array_reverse instead of array_flip.

Flipping before removing duplicates.

Use array_unique to remove duplicates, then array_flip to swap keys and values.

5fill in blank

hard

Fill all three blanks to remove duplicates, flip the array, and then get the keys of the flipped array.

PHP

<?php
$letters = ['x', 'y', 'x', 'z'];
$unique = [1]($letters);
$flipped = [2]($unique);
$keys = [3]($flipped);
print_r($keys);
?>

Drag options to blanks, or click blank then click option'

Aarray_unique

Barray_flip

Carray_keys

Darray_values

Attempts:

3 left

💡 Hint

Common Mistakes

Using array_values instead of array_keys.

Flipping before removing duplicates.

Skipping the step to get keys.

First remove duplicates with array_unique, then flip keys and values with array_flip, and finally get the keys with array_keys.

Practice

1. What does the PHP function array_unique() do to an array?

easy

A. Flips keys and values of the array

B. Removes duplicate values, keeping only the first occurrence

C. Sorts the array in ascending order

D. Removes all values except the last occurrence

Solution

1. Step 1: Understand the purpose of array_unique()

   This function scans the array and removes any duplicate values, but keeps the first time each value appears.

2. Step 2: Compare with other options

   Options B, C, and D describe different functions or behaviors. Only Removes duplicate values, keeping only the first occurrence correctly describes array_unique().

3. Final Answer:

   Removes duplicate values, keeping only the first occurrence -> Option B

4. Quick Check:

   array_unique() removes duplicates = A [OK]

Hint: Remember: unique means no duplicates, keep first [OK]

Common Mistakes:

• Thinking it flips keys and values
• Assuming it sorts the array
• Believing it keeps the last occurrence

2. Which of the following is the correct syntax to flip keys and values of an array $arr in PHP?

easy

A. array_flip($arr);

B. flip_array($arr);

C. array_unique($arr);

D. flip($arr);

Solution

1. Step 1: Identify the correct function name

   The PHP function to swap keys and values is array_flip(). Other options are not valid PHP functions.

2. Step 2: Confirm correct usage

   The syntax is array_flip($arr); which returns a new array with keys and values swapped.

3. Final Answer:

   array_flip($arr); -> Option A

4. Quick Check:

   Flip keys and values = array_flip() [OK]

Hint: Flip keys and values with array_flip() [OK]

Common Mistakes:

• Using non-existent functions like flip_array()
• Confusing array_unique() with array_flip()
• Missing parentheses in function call

3. What is the output of the following PHP code?

$arr = ['a' => 'apple', 'b' => 'banana', 'c' => 'apple'];
$result = array_flip(array_unique($arr));
print_r($result);

medium

A. Array ( [apple] => a [banana] => b )

B. Array ( [a] => apple [b] => banana [c] => apple )

C. Array ( [apple] => c [banana] => b )

D. Array ( [apple] => 0 [banana] => 1 )

Solution

1. Step 1: Apply array_unique() on $arr

   This removes duplicate values, so 'apple' at key 'c' is removed. Result: ['a' => 'apple', 'b' => 'banana']

2. Step 2: Apply array_flip() on the unique array

   Keys and values swap: 'apple' becomes key with value 'a', 'banana' becomes key with value 'b'.

3. Final Answer:

   Array ( [apple] => a [banana] => b ) -> Option A

4. Quick Check:

   Unique then flip = keys and values swapped without duplicates [OK]

Hint: Unique first, then flip keys and values [OK]

Common Mistakes:

• Flipping before removing duplicates
• Expecting duplicate keys in flipped array
• Confusing keys and values in output

4. Consider this PHP code snippet:

$arr = ['x' => 'dog', 'y' => 'cat', 'z' => 'dog'];
$result = array_flip($arr);
print_r($result);

What is the problem with this code?

medium

A. No problem; output will be correct

B. It causes a syntax error because array_flip requires numeric keys

C. array_flip cannot flip string keys

D. The duplicate values cause keys to be overwritten in the flipped array

Solution

1. Step 1: Understand array_flip() behavior with duplicates

   When flipping, values become keys. Duplicate values cause keys to overwrite previous ones.

2. Step 2: Analyze the example

   'dog' appears twice as a value. After flipping, only the last key ('z') remains for 'dog'.

3. Final Answer:

   The duplicate values cause keys to be overwritten in the flipped array -> Option D

4. Quick Check:

   Duplicate values overwrite keys when flipped [OK]

Hint: Duplicates in values overwrite keys after flip [OK]

Common Mistakes:

• Expecting all keys to be preserved
• Thinking array_flip causes syntax errors
• Assuming string keys cannot be flipped

5. You have an array of user IDs with possible duplicates:

$users = [101 => 'alice', 102 => 'bob', 103 => 'alice', 104 => 'carol'];

You want to create a new array where usernames are keys and user IDs are values, but only keep the first occurrence of each username. Which code correctly achieves this?

hard

A. $uniqueUsers = array_flip($users); $uniqueUsers = array_unique($uniqueUsers);

B. $uniqueUsers = array_unique(array_flip($users));

C. $uniqueUsers = array_flip(array_unique($users));

D. $uniqueUsers = array_unique($users); $uniqueUsers = array_unique($uniqueUsers);

Solution

1. Step 1: Remove duplicate usernames with array_unique()

   This keeps the first occurrence of each username, removing duplicates.

2. Step 2: Flip keys and values with array_flip()

   Swaps usernames to keys and user IDs to values, as required.

3. Final Answer:

   $uniqueUsers = array_flip(array_unique($users)); -> Option C

4. Quick Check:

   Unique usernames first, then flip keys and values [OK]

Hint: Unique first, then flip for correct key-value swap [OK]

Common Mistakes:

• Flipping before removing duplicates
• Applying unique after flipping
• Assuming array_unique works on keys