Array merge and combine in PHP - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to merge two arrays using the correct function.

PHP

<?php
$array1 = [1, 2];
$array2 = [3, 4];
$result = [1]($array1, $array2);
print_r($result);
?>

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

Aarray_slice

Barray_combine

Carray_push

Darray_merge

Attempts:

3 left

💡 Hint

Common Mistakes

Using array_combine instead of array_merge

Using array_push which adds elements to an array but does not merge arrays

The array_merge function merges two or more arrays into one.

2fill in blank

medium

Complete the code to combine two arrays into a key-value array.

PHP

<?php
$keys = ['a', 'b'];
$values = [1, 2];
$combined = [1]($keys, $values);
print_r($combined);
?>

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

Aarray_flip

Barray_combine

Carray_slice

Darray_merge

Attempts:

3 left

💡 Hint

Common Mistakes

Using array_merge which just joins arrays

Using array_flip which swaps keys and values

The array_combine function creates an array by using one array for keys and another for values.

3fill in blank

hard

Fix the error in the code to correctly merge arrays with numeric keys.

PHP

<?php
$array1 = [0 => 'apple', 1 => 'banana'];
$array2 = [0 => 'cherry', 1 => 'date'];
$merged = [1]($array1, $array2);
print_r($merged);
?>

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

Aarray_combine

Barray_replace

Carray_merge

Darray_push

Attempts:

3 left

💡 Hint

Common Mistakes

Using array_combine which requires equal length and uses one array as keys

Using array_replace which overwrites values instead of merging

array_merge merges arrays and reindexes numeric keys, so values are appended.

4fill in blank

hard

Fill both blanks to create an array of squares for even numbers only.

PHP

<?php
$numbers = [1, 2, 3, 4, 5];
$squares = [
    [1] => [2]
    for [1] in $numbers if [1] % 2 == 0
];
print_r($squares);
?>

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

A$num

B$num * $num

C$number

D$number * $number

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variable names in the loop and expression

Not squaring the number correctly

We use $num as the variable and square it with $num * $num for even numbers.

5fill in blank

hard

Fill all three blanks to create an associative array with uppercase keys and values greater than 10.

PHP

<?php
$data = ['a' => 5, 'b' => 15, 'c' => 20];
$result = [
    [1] => [2]
    for [1], [2] in $data if [3] > 10
];
print_r($result);
?>

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

A$key

B$value

Dstrtoupper($key)

Attempts:

3 left

💡 Hint

Common Mistakes

Using the same variable name for key and value

Not converting keys to uppercase

We convert keys to uppercase with strtoupper($key) and keep values where $value > 10.

Practice

1. What does the PHP function array_merge do?

easy

A. Creates an associative array from two arrays

B. Joins two or more arrays into one combined array

C. Sorts an array in ascending order

D. Removes duplicate values from an array

Solution

1. Step 1: Understand the purpose of array_merge

   The function array_merge takes multiple arrays and joins their elements into a single array.

2. Step 2: Compare with other functions

   array_combine creates key-value pairs, sorting and removing duplicates are different functions.

3. Final Answer:

   Joins two or more arrays into one combined array -> Option B

4. Quick Check:

   array_merge joins arrays = B [OK]

Hint: array_merge joins arrays end-to-end [OK]

Common Mistakes:

• Confusing array_merge with array_combine
• Thinking array_merge sorts arrays
• Assuming array_merge removes duplicates

2. Which of the following is the correct syntax to combine two arrays into an associative array using array_combine?

easy

A. array_merge($keys, $values);

B. array_combine($values, $keys);

C. array_combine($keys, $values);

D. array_combine($keys);

Solution

1. Step 1: Recall array_combine parameter order

   The first parameter is the array of keys, the second is the array of values.

2. Step 2: Check each option

   array_combine($keys, $values); correctly uses array_combine($keys, $values);. array_combine($values, $keys); reverses parameters, C uses wrong function, D misses second parameter.

3. Final Answer:

   array_combine($keys, $values); -> Option C

4. Quick Check:

   Keys first, values second in array_combine = A [OK]

Hint: Keys go first, values second in array_combine [OK]

Common Mistakes:

• Swapping keys and values parameters
• Using array_merge instead of array_combine
• Missing one of the required parameters

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

$a = [1, 2];
$b = [3, 4];
$result = array_merge($a, $b);
print_r($result);

medium

A. [1, 2, 3, 4]

B. [3, 4, 1, 2]

C. [1 => 2, 3 => 4]

D. Array keys and values combined

Solution

1. Step 1: Understand array_merge behavior

   array_merge joins arrays by appending elements of second array to first, preserving order.

2. Step 2: Apply to given arrays

   $a = [1, 2], $b = [3, 4], merged result is [1, 2, 3, 4].

3. Final Answer:

   [1, 2, 3, 4] -> Option A

4. Quick Check:

   array_merge appends arrays = [1, 2, 3, 4] [OK]

Hint: array_merge appends arrays in order given [OK]

Common Mistakes:

• Thinking array_merge sorts or combines keys
• Confusing output with associative array
• Expecting keys to be preserved as in original arrays

4. Identify the error in this PHP code snippet:

$keys = ['a', 'b'];
$values = [1];
$result = array_combine($keys, $values);
print_r($result);

medium

A. array_combine merges arrays instead of combining keys and values

B. array_combine cannot use string keys

C. array_combine needs only one parameter

D. array_combine requires both arrays to have the same number of elements

Solution

1. Step 1: Check array_combine requirements

   array_combine requires both arrays to have equal length to pair keys and values correctly.

2. Step 2: Analyze given arrays

   $keys has 2 elements, $values has 1 element, causing an error.

3. Final Answer:

   array_combine requires both arrays to have the same number of elements -> Option D

4. Quick Check:

   Equal length arrays needed for array_combine = D [OK]

Hint: Keys and values arrays must be same length [OK]

Common Mistakes:

• Ignoring array length mismatch
• Thinking array_combine works with one array
• Confusing array_combine with array_merge

5. Given two arrays:
$keys = ['name', 'age', 'city'];
$values = ['Alice', 30, 'Paris'];
Which PHP code correctly creates an associative array and then merges it with ['country' => 'France']?

hard

A. $assoc = array_combine($keys, $values); $final = array_merge($assoc, ['country' => 'France']);

B. $assoc = array_merge($keys, $values); $final = array_combine($assoc, ['country' => 'France']);

C. $final = array_combine($keys, $values, ['country' => 'France']);

D. $final = array_merge(array_combine($values, $keys), ['country' => 'France']);

Solution

1. Step 1: Create associative array from keys and values

   Use array_combine($keys, $values) to pair keys with values correctly.

2. Step 2: Merge associative array with another array

   Use array_merge to add the 'country' key-value pair to the associative array.

3. Step 3: Check other options for errors

   $assoc = array_merge($keys, $values); $final = array_combine($assoc, ['country' => 'France']); swaps functions incorrectly, C uses wrong parameter count, D swaps keys and values.

4. Final Answer:

   $assoc = array_combine($keys, $values); $final = array_merge($assoc, ['country' => 'France']); -> Option A

5. Quick Check:

   Combine keys-values, then merge extra array = A [OK]

Hint: Combine keys-values first, then merge extra pairs [OK]

Common Mistakes:

• Swapping keys and values in array_combine
• Trying to combine more than two arrays at once
• Using array_merge before array_combine