PHP implode(): Join Array Elements into a String

implode($separator, $array) joins the values of an array into one string, with $separator between each pair: implode(', ', ['red', 'green', 'blue']) returns "red, green, blue".

<?php
$colors = ['red', 'green', 'blue'];

echo implode(', ', $colors), "\n";
echo implode(' | ', $colors), "\n";
echo implode('', $colors), "\n";

The separator only goes between elements, never before the first or after the last. It is the reverse of explode(), which splits a string into an array.

Syntax

implode(string $separator, array $array): string
implode(array $array): string   // separator defaults to ""

The separator comes first. Older code sometimes passed the array first, implode($array, ', '). That order was deprecated in PHP 7.4 and removed in PHP 8.0, where it throws TypeError: implode(): Argument #2 ($array) must be of type ?array, string given.

implode vs join

join() is an alias of implode(). They take the same arguments and return the same string, so pick one and stay consistent.

<?php
$parts = ['2026', '03', '14'];

echo implode('-', $parts), "\n";
echo join('-', $parts), "\n";
var_dump(implode('-', $parts) === join('-', $parts));

What happens to numbers, booleans and null

Every value is converted to a string first. Numbers print as you would expect, true becomes "1", and false and null become empty strings, which leaves two separators in a row.

<?php
$values = [10, 2.5, true, false, null, 'end'];
echo implode(', ', $values), "\n";

// Remove null and false before joining
$clean = array_filter($values, fn($v) => $v !== null && $v !== false);
echo implode(', ', $clean), "\n";

echo '[', implode(', ', []), "]\n";   // an empty array gives an empty string

Implode an associative array

implode() ignores keys and joins only the values. To get key=value pairs, build each piece with array_map() over the keys and values, then join. http_build_query() does the same for a URL query string and also encodes spaces and special characters.

<?php
$user = ['name' => 'Ada', 'role' => 'admin', 'city' => 'London'];

echo implode(', ', $user), "\n";   // values only

$pairs = array_map(fn($k, $v) => "$k=$v", array_keys($user), $user);
echo implode(', ', $pairs), "\n";

echo http_build_query(['q' => 'php implode', 'page' => 2]), "\n";

The same pattern joins only the keys: implode(', ', array_keys($user)). More on keys and values is on the associative arrays page.

Join with a newline or build an HTML list

The separator can be any string. "\n" (double quotes) puts each value on its own line, which is handy for text files and command line output. With HTML tags as the separator, implode() builds a list in one line. Run the next block and the Page tab shows the rendered list.

<?php
$steps = ['Read the input', 'Validate it', 'Save it'];

$items = array_map('htmlspecialchars', $steps);
echo '<ol><li>' . implode('</li><li>', $items) . '</li></ol>';

Escaping each value with htmlspecialchars() before joining keeps a value like <b> from becoming markup.

Join with "and" before the last item

A human-readable list usually needs "and" before the last element. Pop it off, join the rest, then add it back:

<?php
function humanList(array $items): string
{
    if (count($items) <= 1) {
        return implode('', $items);
    }
    $last = array_pop($items);
    return implode(', ', $items) . ' and ' . $last;
}

echo humanList(['PHP']), "\n";
echo humanList(['PHP', 'Python']), "\n";
echo humanList(['PHP', 'Python', 'Go', 'Rust']), "\n";

Common mistake: nested arrays

implode() works on one level. An element that is itself an array is converted to the word Array, and PHP prints a warning:

<?php
echo implode(', ', ['red', ['orange', 'yellow']]);

Warning: Array to string conversion in /home/index.php on line 2
red, Array

Flatten the inner arrays first, or join each one separately:

<?php
$groups = [
    'warm' => ['red', 'orange'],
    'cool' => ['blue', 'green'],
];

// Join each inner array, then join the results
$lines = array_map(fn($colors) => implode(', ', $colors), $groups);
echo implode("\n", $lines), "\n";

// Or flatten everything into one list
echo implode(', ', array_merge(...array_values($groups))), "\n";