Preg_split for splitting in PHP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of preg_split with simple delimiter

What is the output of the following PHP code?

PHP

<?php
$input = "apple,banana,orange";
$result = preg_split('/,/', $input);
print_r($result);
?>

A Array ( [0] => apple,banana,orange )

B Array ( [0] => apple [1] => banana [2] => orange [3] => )

C Array ( [0] => apple [1] => banana,orange )

D Array ( [0] => apple [1] => banana [2] => orange )

💡 Hint

preg_split splits the string where the pattern matches, returning all parts as array elements.

The pattern '/,/' matches commas, so preg_split splits the string at each comma, producing an array of the fruits.

❓ Predict Output

intermediate

preg_split with limit parameter

What is the output of this PHP code?

PHP

<?php
$input = "one,two,three,four";
$result = preg_split('/,/', $input, 3);
print_r($result);
?>

A Array ( [0] => one [1] => two [2] => three,four )

B Array ( [0] => one [1] => two [2] => three [3] => four )

C Array ( [0] => one,two,three [1] => four )

D Array ( [0] => one [1] => two [2] => three [3] => four [4] => )

💡 Hint

The limit parameter controls how many pieces the string is split into.

With limit=3, preg_split splits into at most 3 parts. The last part contains the rest of the string after the second comma.

❓ Predict Output

advanced

preg_split with PREG_SPLIT_NO_EMPTY flag

What is the output of this PHP code?

PHP

<?php
$input = ",apple,,banana,orange,";
$result = preg_split('/,/', $input, -1, PREG_SPLIT_NO_EMPTY);
print_r($result);
?>

A Array ( [0] => [1] => apple [2] => [3] => banana [4] => orange [5] => )

B Array ( [0] => apple [1] => banana [2] => orange )

C Array ( [0] => apple [1] => [2] => banana [3] => orange )

D Array ( [0] => apple,banana,orange )

💡 Hint

The PREG_SPLIT_NO_EMPTY flag removes empty strings from the result.

The input has empty parts between commas. Using PREG_SPLIT_NO_EMPTY removes those empty strings from the output array.

❓ Predict Output

advanced

preg_split with capturing parentheses

What is the output of this PHP code?

PHP

<?php
$input = "red1green2blue3";
$result = preg_split('/(\d)/', $input, -1, PREG_SPLIT_DELIM_CAPTURE);
print_r($result);
?>

A Array ( [0] => red [1] => 1 [2] => green [3] => 2 [4] => blue [5] => 3 )

B Array ( [0] => red1green2blue3 )

C Array ( [0] => red [1] => green [2] => blue )

D Array ( [0] => red [1] => 1green2blue3 )

💡 Hint

PREG_SPLIT_DELIM_CAPTURE includes the parts matched by parentheses in the output.

The pattern captures digits. With PREG_SPLIT_DELIM_CAPTURE, the digits appear as separate elements in the output array.

🧠 Conceptual

expert

Understanding preg_split behavior with complex regex

Given the code below, how many elements will the resulting array have?

PHP

<?php
$input = "a1b2c3d4";
$result = preg_split('/(?<=\d)/', $input);
echo count($result);
?>

A 7

B 8

C 4

D 1

💡 Hint

The regex uses a lookbehind to split after each digit.

The pattern splits the string after each digit, resulting in 4 parts: 'a1', 'b2', 'c3', 'd4'.

Practice

1. What does the PHP function preg_split do?

easy

A. Counts the number of words in a string.

B. Joins array elements into a string.

C. Replaces parts of a string matching a pattern.

D. Splits a string into parts using a regular expression pattern.

Solution

1. Step 1: Understand the function purpose

   preg_split is designed to split strings based on patterns, not fixed characters.

2. Step 2: Compare options with function behavior

   Only Splits a string into parts using a regular expression pattern. describes splitting using a regular expression pattern, which matches preg_split functionality.

3. Final Answer:

   Splits a string into parts using a regular expression pattern. -> Option D

4. Quick Check:

   preg_split splits string by regex pattern = A [OK]

Hint: Remember: preg_split uses regex to split strings [OK]

Common Mistakes:

• Confusing preg_split with implode or join functions
• Thinking preg_split replaces text instead of splitting
• Assuming preg_split counts words

2. Which of the following is the correct syntax to split a string by commas using preg_split?

easy

A. preg_split('/,/', $string);

B. preg_split(',', $string);

C. preg_split($string, '/,/');

D. preg_split($string, ',');

Solution

1. Step 1: Identify correct parameter order

   The first parameter of preg_split is the regex pattern as a string, the second is the input string.

2. Step 2: Check regex pattern format

   The pattern must be enclosed in delimiters like slashes /, /. preg_split('/,/', $string); uses this correctly.

3. Final Answer:

   preg_split('/,/', $string); -> Option A

4. Quick Check:

   Pattern first with slashes, then string = B [OK]

Hint: Pattern goes first with slashes, then the string [OK]

Common Mistakes:

• Omitting regex delimiters like slashes
• Swapping the order of parameters
• Using plain string instead of regex pattern

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

$text = "apple,banana;orange|grape";
$result = preg_split('/[,;|]/', $text);
print_r($result);

medium

A. ["apple,banana;orange|grape"]

B. ["apple", "banana;orange|grape"]

C. ["apple", "banana", "orange", "grape"]

D. ["apple", "banana", "orange|grape"]

Solution

1. Step 1: Understand the regex pattern

   The pattern /[,;|]/ matches any comma, semicolon, or pipe character as separators.

2. Step 2: Split the string by these separators

   The string splits at each comma, semicolon, and pipe, resulting in four parts: "apple", "banana", "orange", "grape".

3. Final Answer:

   ["apple", "banana", "orange", "grape"] -> Option C

4. Quick Check:

   Split by , ; | = ["apple", "banana", "orange", "grape"] [OK]

Hint: Regex with multiple separators splits into all parts [OK]

Common Mistakes:

• Not recognizing all separators in regex
• Expecting only comma to split
• Confusing output format with string instead of array

4. The following code is intended to split a string by spaces, but it causes an error. What is the problem?

$str = "one two three";
$parts = preg_split(' ', $str);
print_r($parts);

medium

A. The print_r function is used incorrectly.

B. The pattern is missing regex delimiters.

C. preg_split cannot split by spaces.

D. The string variable is empty.

Solution

1. Step 1: Check the pattern parameter

   The pattern passed is a plain space character without regex delimiters, which is invalid syntax for preg_split.

2. Step 2: Correct pattern format

   Regex patterns must be enclosed in delimiters like slashes, e.g., '/ /' to match a space.

3. Final Answer:

   The pattern is missing regex delimiters. -> Option B

4. Quick Check:

   Regex pattern needs delimiters like slashes [OK]

Hint: Always wrap regex pattern in delimiters like slashes [OK]

Common Mistakes:

• Using plain string without delimiters as pattern
• Assuming preg_split works like explode for spaces
• Blaming print_r for output issues

5. You want to split a string by any number of spaces or commas, but ignore empty parts in the result. Which preg_split call achieves this?

hard

A. preg_split('/[ ,]+/', $string, -1, PREG_SPLIT_NO_EMPTY);

B. preg_split('/[ ,]/', $string);

C. preg_split('/[ ,]+/', $string);

D. preg_split('/[ ,]+/', $string, 0);

Solution

1. Step 1: Understand the pattern and flags

   The pattern /[ ,]+/ matches one or more spaces or commas, so it splits on any group of these separators.

2. Step 2: Use flag to remove empty parts

   The flag PREG_SPLIT_NO_EMPTY tells preg_split to exclude empty strings from the result array.

3. Step 3: Check other options

   preg_split('/[ ,]/', $string); splits on single separators but may leave empty parts. preg_split('/[ ,]+/', $string); does not remove empty parts. preg_split('/[ ,]+/', $string, 0); uses 0 as limit which is invalid.

4. Final Answer:

   preg_split('/[ ,]+/', $string, -1, PREG_SPLIT_NO_EMPTY); -> Option A

5. Quick Check:

   Use + for multiple separators and NO_EMPTY flag [OK]

Hint: Use + in pattern and PREG_SPLIT_NO_EMPTY flag [OK]

Common Mistakes:

• Not using + to match multiple separators
• Forgetting PREG_SPLIT_NO_EMPTY to remove blanks
• Using invalid limit parameter