Implode and join in PHP - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the implode() function do in PHP?

The implode() function joins array elements into a single string using a specified separator.

beginner

Is join() different from implode() in PHP?

No, join() is an alias of implode(). Both do the same thing: join array elements into a string.

beginner

How do you use implode() to join array elements with a comma?

Use implode(",", $array). This joins all elements of $array separated by commas.

beginner

What happens if you call implode() with an empty array?

It returns an empty string because there are no elements to join.

intermediate

Can implode() be used without specifying a separator?

Yes, if you omit the separator, PHP uses an empty string as default, joining elements directly without anything between them.

What is the output of implode('-', ['a', 'b', 'c'])?

A "a-b-c"

B "abc"

C "a,b,c"

D "a b c"

The implode() function joins array elements with the given separator, here a dash '-'.

Which function is an alias of implode() in PHP?

A explode()

B concat()

C join()

D split()

join() is an alias of implode(), both join array elements into a string.

What does implode() return when given an empty array?

A empty string ""

B false

C null

D array

When the array is empty, implode() returns an empty string.

What is the default separator if none is provided to implode()?

A comma

B empty string

C space

D semicolon

If no separator is given, implode() uses an empty string to join elements.

Which of these is a correct way to join array elements with a space using implode()?

A implode($array, ' ')

B implode($array)

C join($array, ' ')

D implode(' ', $array)

The correct syntax is implode(' ', $array) where the first argument is the separator.

Explain how implode() works and give an example of joining an array with commas.

Think about how you combine words with commas in a sentence.

Describe the relationship between implode() and join() in PHP.

They are like two names for the same thing.

Practice

1. What does the PHP function implode do when used with an array?

easy

A. It splits a string into an array based on a separator.

B. It joins array elements into a single string with a separator.

C. It sorts the array elements alphabetically.

D. It removes duplicate elements from the array.

Solution

1. Step 1: Understand the purpose of implode

   The implode function takes an array and joins its elements into one string.

2. Step 2: Recognize the role of the separator

   You can specify a separator string to put between elements in the resulting string.

3. Final Answer:

   It joins array elements into a single string with a separator. -> Option B

4. Quick Check:

   implode joins array elements [OK]

Hint: Remember: implode combines array items into one string [OK]

Common Mistakes:

• Confusing implode with explode (which splits strings)
• Thinking implode sorts or filters arrays
• Assuming implode returns an array

2. Which of the following is the correct syntax to join array elements with a comma using implode?

easy

A. implode(',', $array);

B. implode($array, ',');

C. implode($array);

D. implode(',', array);

Solution

1. Step 1: Recall the correct parameter order of implode

   The first parameter is the separator string, the second is the array.

2. Step 2: Check each option's syntax

   implode(',', $array); uses implode(',', $array); which is correct syntax.

3. Final Answer:

   implode(',', $array); -> Option A

4. Quick Check:

   Separator first, array second in implode [OK]

Hint: Separator goes first, array second in implode [OK]

Common Mistakes:

• Swapping the order of parameters
• Using variable name without $ sign
• Omitting the array parameter

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

$arr = ['apple', 'banana', 'cherry'];
echo implode(' - ', $arr);

medium

A. apple -banana -cherry

B. apple, banana, cherry

C. apple - banana - cherry

D. applebanana cherry

Solution

1. Step 1: Understand implode with ' - ' separator

   The separator string ' - ' is placed between each array element.

2. Step 2: Join the array elements

   Joining 'apple', 'banana', 'cherry' with ' - ' results in 'apple - banana - cherry'.

3. Final Answer:

   apple - banana - cherry -> Option C

4. Quick Check:

   implode with ' - ' joins elements with that exact separator [OK]

Hint: Check the separator string carefully in output [OK]

Common Mistakes:

• Confusing separator with comma
• Missing spaces around separator
• Assuming implode adds extra spaces

4. Identify the error in this PHP code snippet:

$fruits = ['apple', 'banana', 'cherry'];
echo implode($fruits, ', ');

medium

A. implode cannot be used with arrays.

B. The array variable is missing the $ sign.

C. The separator must be an array, not a string.

D. The separator and array parameters are swapped in implode.

Solution

1. Step 1: Check parameter order in implode

   implode expects separator first, then array second.

2. Step 2: Analyze given code

   Code uses implode($fruits, ', '); which swaps parameters.

3. Final Answer:

   The separator and array parameters are swapped in implode. -> Option D

4. Quick Check:

   Parameter order matters in implode [OK]

Hint: Separator first, array second in implode [OK]

Common Mistakes:

• Swapping parameters order
• Assuming implode works like explode
• Using wrong variable names

5. You have an array $words = ['one', '', 'three', null, 'five'];. You want to join only the non-empty, non-null elements with a comma. Which code correctly does this?

hard

A. $filtered = array_filter($words); echo implode(', ', $filtered);

B. echo implode(', ', $words);

C. $filtered = array_map(trim, $words); echo implode(', ', $filtered);

D. $filtered = array_filter($words, fn($w) => $w !== ''); echo implode(', ', $filtered);

Solution

1. Step 1: Remove empty and null elements using array_filter

   array_filter without callback removes falsy values like empty string and null.

2. Step 2: Use implode to join filtered array with comma

   Joining filtered elements with ', ' produces the desired string.

3. Final Answer:

   $filtered = array_filter($words); echo implode(', ', $filtered); -> Option A

4. Quick Check:

   array_filter removes empty/null, then implode joins [OK]

Hint: Filter falsy values before implode to exclude empties [OK]

Common Mistakes:

• Using implode directly without filtering
• Using array_map(trim) which doesn't remove null
• Filtering only empty strings but not null