Array key and value extraction in PHP - Step-by-Step Execution

Concept Flow - Array key and value extraction

Start with array

↓

Extract keys

→Store keys in new array

↓

Extract values

→Store values in new array

↓

Use keys and values separately

We start with an array, then extract its keys and values into separate arrays to use them individually.

Execution Sample

PHP

<?php
$array = ['a' => 1, 'b' => 2, 'c' => 3];
$keys = array_keys($array);
$values = array_values($array);
print_r($keys);
print_r($values);
?>

This code extracts keys and values from an associative array and prints them separately.

Execution Table

Step	Action	Array State	Result	Output
1	Define array	['a' => 1, 'b' => 2, 'c' => 3]	Array created
2	Extract keys	['a' => 1, 'b' => 2, 'c' => 3]	['a', 'b', 'c']
3	Extract values	['a' => 1, 'b' => 2, 'c' => 3]	[1, 2, 3]
4	Print keys	keys = ['a', 'b', 'c']	keys array	Array ( [0] => a [1] => b [2] => c )
5	Print values	values = [1, 2, 3]	values array	Array ( [0] => 1 [1] => 2 [2] => 3 )

💡 All keys and values extracted and printed.

Variable Tracker

Variable	Start	After Step 2	After Step 3	Final
$array	undefined	['a' => 1, 'b' => 2, 'c' => 3]	['a' => 1, 'b' => 2, 'c' => 3]	['a' => 1, 'b' => 2, 'c' => 3]
$keys	undefined	['a', 'b', 'c']	['a', 'b', 'c']	['a', 'b', 'c']
$values	undefined	undefined	[1, 2, 3]	[1, 2, 3]

Key Moments - 2 Insights

Why do keys become a simple list of strings instead of keeping their original association?

Because array_keys() returns only the keys as a plain indexed array, losing the original key-value association, as shown in step 2 of the execution_table.

Why do values become a zero-based indexed array instead of keeping their original keys?

Because array_values() returns only the values as a plain indexed array starting at 0, ignoring original keys, as seen in step 3 of the execution_table.

Visual Quiz - 3 Questions

Look at the execution_table at step 2, what is the content of $keys?

A ['a' => 1, 'b' => 2, 'c' => 3]

B ['1', '2', '3']

C ['a', 'b', 'c']

D [1, 2, 3]

💡 Hint

Check the 'Result' column at step 2 in execution_table.

At which step does $values get assigned its array?

A Step 3

B Step 2

C Step 1

D Step 4

💡 Hint

Look at variable_tracker for $values and see when it changes from undefined.

If the original array had numeric keys, how would array_keys() output look?

A An array of values

B An array of those numeric keys

C An associative array with keys and values swapped

D An empty array

💡 Hint

array_keys() always returns the keys as a simple indexed array, regardless of key type.

Concept Snapshot

PHP arrays have keys and values.
Use array_keys() to get all keys as a simple list.
Use array_values() to get all values as a simple list.
Both functions return indexed arrays starting at 0.
Useful to separate keys and values for processing.

Full Transcript

We start with an associative array with keys 'a', 'b', 'c' and values 1, 2, 3. Using array_keys(), we extract the keys into a new indexed array ['a', 'b', 'c']. Using array_values(), we extract the values into a new indexed array [1, 2, 3]. We print both arrays to see the separated keys and values. This helps when you want to work with keys and values separately in PHP.

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