Array merge and combine in PHP - Mini Project: Build & Apply

Array merge and combine

📖 Scenario: You are organizing a small event and have two lists: one with guest names and another with their favorite drinks. You want to create a combined list that pairs each guest with their favorite drink.

🎯 Goal: Build a PHP script that merges two arrays into one associative array where each guest's name is linked to their favorite drink.

📋 What You'll Learn

Create two arrays with exact values for guests and drinks

Create a variable to hold the combined array

Use the array_combine function to merge the two arrays

Print the combined array using print_r

💡 Why This Matters

🌍 Real World

Combining related lists like names and preferences is common in event planning, surveys, and data organization.

💼 Career

Understanding how to merge arrays is useful for backend developers managing user data, preferences, or configuration settings.

1

Create the guests and drinks arrays

Create an array called $guests with these exact values: 'Alice', 'Bob', 'Charlie'. Also create an array called $drinks with these exact values: 'Coffee', 'Tea', 'Juice'.

PHP

<?php
// Create the $guests array with 'Alice', 'Bob', 'Charlie'
// Create the $drinks array with 'Coffee', 'Tea', 'Juice'

Hint

Use square brackets [] to create arrays in PHP.

2

Create a variable for the combined array

Create a variable called $guest_drinks and set it to null for now.

PHP

<?php
$guests = ['Alice', 'Bob', 'Charlie'];
$drinks = ['Coffee', 'Tea', 'Juice'];
// Create $guest_drinks variable and set it to null

Hint

Initialize the variable with null before assigning the combined array.

3

Combine the guests and drinks arrays

Use the array_combine function to combine $guests and $drinks into $guest_drinks.

PHP

<?php
$guests = ['Alice', 'Bob', 'Charlie'];
$drinks = ['Coffee', 'Tea', 'Juice'];
$guest_drinks = null;
// Combine $guests and $drinks into $guest_drinks

Hint

The array_combine function takes two arrays: keys and values.

4

Print the combined array

Print the $guest_drinks array using print_r to show the combined list.

PHP

<?php
$guests = ['Alice', 'Bob', 'Charlie'];
$drinks = ['Coffee', 'Tea', 'Juice'];
$guest_drinks = null;
$guest_drinks = array_combine($guests, $drinks);
// Print the $guest_drinks array

Hint

Use print_r($guest_drinks); to display the array in a readable format.

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