Array sort functions in PHP - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the sort() function do in PHP?

The sort() function sorts an array in ascending order and reindexes the keys starting from 0.

beginner

How does asort() differ from sort()?

asort() sorts an array in ascending order but preserves the original keys, unlike sort() which reindexes keys.

beginner

What is the purpose of ksort() in PHP?

ksort() sorts an array by its keys in ascending order, keeping the key-value association intact.

intermediate

Explain the difference between rsort() and arsort().

rsort() sorts an array in descending order and reindexes keys, while arsort() sorts in descending order but preserves the original keys.

intermediate

What does krsort() do?

krsort() sorts an array by its keys in descending order, preserving key-value pairs.

Which PHP function sorts an array by values in ascending order and preserves keys?

A ksort()

B sort()

C asort()

D rsort()

asort() sorts values ascending and keeps keys unchanged.

What happens to keys when you use sort() on an array?

A Keys are preserved

B Keys are sorted

C Keys are removed

D Keys are reindexed starting from 0

sort() reindexes keys starting from 0 after sorting.

Which function sorts an array by keys in descending order?

A krsort()

B ksort()

C arsort()

D rsort()

krsort() sorts keys descending, preserving key-value pairs.

If you want to sort an array by values in descending order and keep keys, which function do you use?

A rsort()

B arsort()

C sort()

D asort()

arsort() sorts values descending and preserves keys.

Which function would you use to sort an array by keys in ascending order?

A ksort()

B asort()

C sort()

D arsort()

ksort() sorts keys ascending, preserving key-value pairs.

Describe the difference between sort() and asort() in PHP.

Think about what happens to the keys after sorting.

Explain when you would use ksort() versus sort().

Consider whether you want to sort by keys or values.

Practice

1. Which PHP function sorts an array and keeps the original keys intact?

easy

A. rsort()

B. sort()

C. ksort()

D. asort()

Solution

1. Step 1: Understand key preservation in sorting

   asort() sorts values but keeps the original keys unchanged.

2. Step 2: Compare with other functions

   sort() resets keys, rsort() sorts in reverse but resets keys, ksort() sorts by keys, not values.

3. Final Answer:

   asort() -> Option D

4. Quick Check:

   Keep keys while sorting values = asort() [OK]

Hint: Use asort() to sort values and keep keys unchanged [OK]

Common Mistakes:

• Confusing sort() with asort() for key preservation
• Thinking ksort() sorts by values
• Assuming rsort() keeps keys

2. Which of the following is the correct syntax to sort an array in ascending order and reset keys in PHP?

easy

A. asort($array);

B. sort($array);

C. ksort($array);

D. arsort($array);

Solution

1. Step 1: Identify function for ascending sort with key reset

   sort() sorts array values in ascending order and resets keys.

2. Step 2: Check other options

   asort() keeps keys, ksort() sorts by keys, arsort() sorts descending.

3. Final Answer:

   sort($array); -> Option B

4. Quick Check:

   Ascending sort with reset keys = sort() [OK]

Hint: Use sort() to sort ascending and reset keys [OK]

Common Mistakes:

• Using asort() when keys should reset
• Confusing ksort() with value sort
• Using arsort() for ascending order

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

$arr = [3 => 'apple', 1 => 'banana', 2 => 'cherry'];
sort($arr);
print_r($arr);

medium

A. [0 => 'apple', 1 => 'banana', 2 => 'cherry']

B. [1 => 'banana', 2 => 'cherry', 3 => 'apple']

C. [0 => 'banana', 1 => 'cherry', 2 => 'apple']

D. [0 => 'apple', 1 => 'cherry', 2 => 'banana']

Solution

1. Step 1: Understand sort() behavior on keys

   sort() sorts values ascending and resets keys starting from 0.

2. Step 2: Sort values and assign new keys

   Values sorted ascending: 'apple', 'banana', 'cherry'. Keys reset to 0,1,2 respectively.

3. Final Answer:

   [0 => 'apple', 1 => 'banana', 2 => 'cherry'] -> Option A

4. Quick Check:

   sort() resets keys and sorts ascending [OK]

Hint: sort() resets keys and sorts values ascending [OK]

Common Mistakes:

• Expecting original keys to remain
• Confusing sort() with asort()
• Mixing order of sorted values

4. Identify the error in the following PHP code snippet:

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

medium

A. ksort() sorts values, not keys

B. Array keys must be numeric for ksort()

C. ksort() does not accept SORT_DESC as a parameter

D. print_r() cannot print associative arrays

Solution

1. Step 1: Check ksort() parameters

   ksort() sorts array by keys in ascending order only; it does not support descending order.

2. Step 2: Understand SORT_DESC usage

   SORT_DESC is invalid for ksort(); to sort keys descending, use krsort() instead.

3. Final Answer:

   ksort() does not accept SORT_DESC as a parameter -> Option C

4. Quick Check:

   ksort() only sorts keys ascending [OK]

Hint: Use krsort() for descending key sort, not ksort() [OK]

Common Mistakes:

• Passing SORT_DESC to ksort()
• Thinking ksort() sorts values
• Believing print_r() can't print associative arrays

5. You have an associative array with user IDs as keys and scores as values:

$scores = [101 => 50, 102 => 75, 103 => 50, 104 => 90];

You want to sort the array by scores in descending order but keep the user IDs as keys. Which function should you use?

hard

A. arsort()

B. rsort()

C. krsort()

D. sort()

Solution

1. Step 1: Identify sorting by values descending with keys preserved

   arsort() sorts array by values in descending order and keeps keys intact.

2. Step 2: Compare with other functions

   rsort() sorts values descending but resets keys, krsort() sorts keys descending, sort() sorts ascending and resets keys.

3. Final Answer:

   arsort() -> Option A

4. Quick Check:

   Sort values descending and keep keys = arsort() [OK]

Hint: Use arsort() to sort values descending and keep keys [OK]

Common Mistakes:

• Using rsort() which resets keys
• Confusing krsort() with value sort
• Using sort() which sorts ascending and resets keys