Array key and value extraction in PHP - Mini Project: Build & Apply

Array key and value extraction

📖 Scenario: You have a list of products with their prices stored in an array. You want to separate the product names and their prices into two different arrays for easier use later.

🎯 Goal: Build a PHP script that extracts the keys (product names) and values (prices) from an associative array into two separate arrays.

📋 What You'll Learn

Create an associative array called $products with exact entries: 'Apple' => 150, 'Banana' => 50, 'Cherry' => 200

Create a variable called $productNames to hold the keys from $products

Create a variable called $productPrices to hold the values from $products

Print the $productNames array

Print the $productPrices array

💡 Why This Matters

🌍 Real World

Extracting keys and values from arrays is common when working with data like product lists, user information, or settings.

💼 Career

Many jobs require handling associative arrays or dictionaries to organize and process data efficiently.

1

Create the products array

Create an associative array called $products with these exact entries: 'Apple' => 150, 'Banana' => 50, 'Cherry' => 200.

PHP

# Your code here

Hint

Use square brackets [] to create the array and separate each key-value pair with a comma.

2

Extract the product names

Create a variable called $productNames and set it to the keys of the $products array using the array_keys() function.

PHP

 150, 'Banana' => 50, 'Cherry' => 200];
# Your code here

Hint

Use the array_keys() function to get all keys from an array.

3

Extract the product prices

Create a variable called $productPrices and set it to the values of the $products array using the array_values() function.

PHP

 150, 'Banana' => 50, 'Cherry' => 200];
$productNames = array_keys($products);
# Your code here

Hint

Use the array_values() function to get all values from an array.

4

Print the product names and prices

Print the $productNames array and then print the $productPrices array using print_r().

PHP

 150, 'Banana' => 50, 'Cherry' => 200];
$productNames = array_keys($products);
$productPrices = array_values($products);
# Your code here

Hint

Use print_r() to display arrays in a readable format.

Practice

1. Which PHP function is used to extract all the keys from an array?

easy

A. array_map()

B. array_values()

C. array_keys()

D. array_filter()

Solution

1. Step 1: Understand the function purpose

   array_keys() returns all keys from an array.

2. Step 2: Compare with other functions

   array_values() returns values, not keys; others do different tasks.

3. Final Answer:

   array_keys() -> Option C

4. Quick Check:

   Keys extraction = array_keys() [OK]

Hint: Keys come from array_keys(), values from array_values() [OK]

Common Mistakes:

• Confusing array_keys() with array_values()
• Using array_map() to get keys
• Trying to get keys with array_filter()

2. Which of the following is the correct syntax to get all values from an array $arr in PHP?

easy

A. array_values($arr);

B. array_keys($arr);

C. values_array($arr);

D. get_values($arr);

Solution

1. Step 1: Identify the correct function name

   The function to get values is array_values().

2. Step 2: Check syntax correctness

   Correct syntax is array_values($arr); with parentheses and variable inside.

3. Final Answer:

   array_values($arr); -> Option A

4. Quick Check:

   Values extraction = array_values() [OK]

Hint: Values come from array_values(), keys from array_keys() [OK]

Common Mistakes:

• Using array_keys() to get values
• Using non-existent functions like values_array()
• Missing parentheses in function call

3. What will be the output of the following PHP code?

$arr = ['a' => 1, 'b' => 2, 'c' => 3];
print_r(array_keys($arr));

medium

A. Array ( [0] => 1 [1] => 2 [2] => 3 )

B. Array ( [0] => 'a' [1] => 'b' [2] => 'c' )

C. Array ( [a] => 1 [b] => 2 [c] => 3 )

D. Array ( [0] => a [1] => b [2] => c )

Solution

1. Step 1: Understand array_keys() output

   It returns an indexed array of all keys from the input array.

2. Step 2: Analyze given array keys

   Keys are strings 'a', 'b', 'c', so output is an indexed array with these strings.

3. Final Answer:

   Array ( [0] => a [1] => b [2] => c ) -> Option D

4. Quick Check:

   array_keys(['a'=>1,...]) = ['a','b','c'] [OK]

Hint: array_keys() returns keys as indexed array [OK]

Common Mistakes:

• Confusing keys with values in output
• Expecting associative array output
• Including quotes in output keys

4. Identify the error in this PHP code snippet:

$arr = ['x' => 10, 'y' => 20];
$keys = array_values($arr);
print_r($keys);

medium

A. array_values() should be array_keys() to get keys

B. Missing semicolon after array declaration

C. print_r() cannot print arrays

D. Variable $keys is not defined

Solution

1. Step 1: Understand the goal

   The code tries to get keys but uses array_values() which returns values.

2. Step 2: Correct function usage

   To get keys, use array_keys() instead of array_values().

3. Final Answer:

   array_values() should be array_keys() to get keys -> Option A

4. Quick Check:

   Keys need array_keys(), not array_values() [OK]

Hint: Use array_keys() for keys, array_values() for values [OK]

Common Mistakes:

• Mixing up array_keys() and array_values()
• Assuming print_r() can't print arrays
• Ignoring correct variable definitions

5. Given the array $data = ['apple' => 3, 'banana' => 0, 'cherry' => 5, 'date' => 0];, which PHP code correctly extracts only the keys with non-zero values?

hard

A. $keys = array_keys($data);

B. $keys = array_keys(array_filter($data));

C. $keys = array_values(array_filter($data));

D. $keys = array_filter(array_keys($data));

Solution

1. Step 1: Filter array to keep non-zero values

   array_filter($data) removes entries with zero values.

2. Step 2: Extract keys from filtered array

   array_keys() gets keys from the filtered array, giving only keys with non-zero values.

3. Final Answer:

   $keys = array_keys(array_filter($data)); -> Option B

4. Quick Check:

   Filter then keys = array_keys(array_filter()) [OK]

Hint: Filter first, then get keys with array_keys(array_filter()) [OK]

Common Mistakes:

• Using array_values() instead of array_keys() after filtering
• Not filtering before extracting keys
• Filtering keys instead of values