String concatenation vs array implode in PHP

Question

Having used Java for a long time my standard method for creating long strings piece by piece was to add the elements to an array and then implode the array.

$out[] = 'a';
$out[] = 'b';
echo implode('', $out);

But then with a lot of data.

The (standard PHP) alternative is to use string concatenation.

$out = 'a';
$out .= 'b';
echo $out;

To my surprise there seems to be no speed difference between both methods. When there is significant time difference usually it is the concatenation that seems faster, but not all of the time.

So my question is: are there - apart from style and code readability - any other reasons to choose one approach over the other?

PHP ist not Java. So don’t be surprised that they differ.

Gumbo
– Gumbo

2009-12-04 14:54:33 +00:00
Commented Dec 4, 2009 at 14:54 — Gumbo
– Gumbo, Commented Dec 4, 2009 at 14:54
In PHP, Strings are not immutable or even objects.

Powerlord
– Powerlord

2009-12-04 14:57:28 +00:00
Commented Dec 4, 2009 at 14:57 — Powerlord
– Powerlord, Commented Dec 4, 2009 at 14:57

Scott Saunders · Accepted Answer · 2009-12-04 14:49:33Z

9

To me, using an array implies that you're going to do something that can't be done with simple string concatenation. Like sorting, checking for uniqueness, etc. If you're not doing anything like that, then string concatenation will be easier to read in a year or two by someone who doesn't know the code. They won't have to wonder whether the array is going to be manipulated before imploded.

That said, I take the imploded array approach when I need to build up a string with commas or " and " between words.

answered Dec 4, 2009 at 14:49

Scott Saunders

30.5k14 gold badges60 silver badges66 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

erenon · Accepted Answer · 2009-12-04 14:43:09Z

4

Choose the more readable one. Always. This case, i would pick up the second apporach. Then optimize it, if it's a bottleneck.

answered Dec 4, 2009 at 14:43

erenon

19.2k2 gold badges65 silver badges97 bronze badges

3 Comments

Matijs Over a year ago

No it is not a bottleneck, just curious. Anyhow I already mentioned readability.

johannes Over a year ago

I can only agree to this - never do something since a micro-benchmark shows it's 0.0001% faster. with XDebug or zendDebugger there are profilers for PHP and if that's not enough there are ways to profile the PHP runtime too, time spent there is way better used than in maintianing "optmized" code (and often it's even cheaper to run some more hardware than paying the developer)

Ben James Over a year ago

+1 just choose the most appropriate one. If implode solves the problem elegantly, use it.

Duroth · Accepted Answer · 2009-12-04 14:52:50Z

3

One (subtle) difference is clearly visible when generating a character-seperated string:

<?php
$out[] = 'a';
$out[] = 'b';
echo implode(',', $out);

foreach($out as $o) {
    echo $o . ',';
}

?>

The first one will print a,b where the latter will print a,b,. So unless you're using an empty string as a seperator, as you did in your example, it's usually preferred to use implode().

answered Dec 4, 2009 at 14:52

Duroth

6,5812 gold badges22 silver badges23 bronze badges

2 Comments

Adam Raney Over a year ago

One could do: $first = true; foreach ($out as $o) { if ($first) $first = false; else echo ','; echo $o; } That should give you a,b instead.

Lukman Over a year ago

@Raney: why all the trouble when implode() way is easier?

Lucas Oman · Accepted Answer · 2009-12-04 14:55:12Z

2

The concatenation-vs-implode holy war aside: No, there is no difference.

answered Dec 4, 2009 at 14:55

Lucas Oman

15.9k2 gold badges47 silver badges45 bronze badges

Comments

Andriy Makukha · Accepted Answer · 2021-05-29 07:33:39Z

2

Here is a performance test for both approaches:

<?php

const M = 1000000;

// Imploding method
$start = microtime(true);
$arr = [];
for ($i = 0; $i < M; $i++) {
    $arr[] = chr(65 + ($i & 0x7));
}
$str1 = implode('', $arr);
$time1 = microtime(true) - $start;

// Concatenation method
$start = microtime(true);
$str2 = '';
for ($i = 0; $i < M; $i++) {
    $str2 .= chr(65 + ($i & 0x7));
}
$time2 = microtime(true) - $start;

assert( $str1 == $str2 ); 
echo "Time 1: $time1\n";
echo "Time 2: $time2\n";

Output with PHP 7.1.33 on MacOS:

Time 1: 0.121246
Time 2: 0.059228

Output with PHP 8.0.5 on a (slow) Debian:

Time 1: 0.88076496124268
Time 2: 0.8109610080719

So, concatenation method works faster.

answered May 29, 2021 at 7:33

Andriy Makukha

8,5041 gold badge48 silver badges57 bronze badges

Comments

Raz · Accepted Answer · 2009-12-04 14:55:41Z

0

it depends on what you want to do with the string / array and how you create it

if you start with an array and need to sort it / manipulate certain elements, then i suggest implode

other than that i usually use concatenation

answered Dec 4, 2009 at 14:55

Raz

6921 gold badge8 silver badges19 bronze badges

Collectives™ on Stack Overflow

String concatenation vs array implode in PHP

6 Answers 6

Comments

3 Comments

2 Comments

Comments

Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

6 Answers 6

Comments

3 Comments

2 Comments

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related