PHP unset not removing value from array loop

Question

I have an array("https", "www", "stackoverflow", "com")

$search_array = array("https", "www", "stackoverflow", "com");

for ($i=0; $i < count($search_array); $i++) { 
    if (
        $search_array[$i] == null ||
        strtolower($search_array[$i]) == "http" && count($search_array) > 1 ||
        strtolower($search_array[$i]) == "https" && count($search_array) > 1 ||
        strtolower($search_array[$i]) == "www" && count($search_array) > 1 ||
        strtolower($search_array[$i]) == "com" && count($search_array) > 1
    ) unset($search_array[$i]);
}

die(print_r($search_array));

I want the result array("stackoverflow");, but im getting the result array("stackoverflow", "com"); any idea?

What have you tried to resolve the problem? Where are you stuck? That's so little code that you should be able to dump the values in each iteration and check them — Nico Haase
– Nico Haase, Commented Nov 7, 2022 at 16:51
@NicoHaase Its not removing the "com" from the array even tho i belive the code is correct? — Natro90
– Natro90, Commented Nov 7, 2022 at 16:52
This isn't a solution per-se, but your code works perfect when using a foreach() instead of a for() loop: foreach($search_array as $i => $domain) { (3v4l.org/41FYo for reference) — Tim Lewis
– Tim Lewis, Commented Nov 7, 2022 at 16:55
@TimLewis i have realised its down to the count($search_array), the count will go down in each for loop. thanks — Natro90
– Natro90, Commented Nov 7, 2022 at 16:59
Yeah exactly, the count goes down and iteration stops. $c = count($search_array); for ($i=0; $i < $c; $i++) {. Just do the count before the loop. (Also, in general a good idea to avoid functions in a loop condition, waste of cycles to re-evaluate at each loop.) — Markus AO
– Markus AO, Commented Nov 7, 2022 at 17:02

Tim Lewis · Accepted Answer · 2022-11-07 17:03:05Z

1

As pointed out in the comments and other answers, you have an issue when looping and unset()-ing. The answers show how to handle this when using a for() loop, but you can also simply use a foreach():

$search_array = array("https", "www", "stackoverflow", "com");

foreach($search_array as $i => $domain) { 
    if (
        $domain == null ||
        $domain == "http" && count($search_array) > 1 ||
        $domain == "https" && count($search_array) > 1 ||
        $domain == "www" && count($search_array) > 1 ||
        $domain == "com" && count($search_array) > 1
    ) { 
        unset($search_array[$i]);
    }
}

die(print_r($search_array));

Output from this approach is:

Array ( [2] => stackoverflow )

answered Nov 7, 2022 at 17:03

Tim Lewis

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Comments

nevada_scout · Accepted Answer · 2022-11-07 17:00:01Z

You are modifying the array while looping around it. This causes the for loop to not run for all of the elements inside it. You can verify this by calling echo $i where you currently do unset().

Also your if statements need brackets around them to ensure that the && and || run in the correct order.

To get the result you want, create a new array of the valid values that you want to save:

<?php
$search_array = array("https", "www", "stackoverflow", "com");
$result_array = array();

for ($i = 0; $i < count($search_array); $i++) {
    $item = strtolower($search_array[$i]);
    
    if (
        isset($search_array[$i])
        && $item !== "http"
        && $item !== "https"
        && $item !== "www"
        && $item !== "com"
    ) {
        $result_array[] = $item;
    }
}


var_dump($result_array);   // Result => "stackoverflow"

fseydel · Accepted Answer · 2022-11-07 17:01:13Z

1

You're changing the value of your loop exit condition inside your loop - which is usually a bad idea. On unsetting the array value, the array length gets lower, and thus the last iteration is never run.

first run (after unset): $i=0; $search_array = array("www", "stackoverflow", "com"); count($search_array)=3

second run (after unset): $i=1; $search_array = array("stackoverflow", "com"); count($search_array)=2

now your loop won't run again, as next $i would be 2, and this is now triggering your exit condition...

answered Nov 7, 2022 at 17:01

fseydel

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Comments

arkascha · Accepted Answer · 2022-11-07 17:03:08Z

1

In addition to what others here correctly point out and demonstrate I would like to suggest to take a somewhat more direct approach: always use the right tool for your task.

What you are trying to do is filter the input array, right? Then why don't you use the array_filter() function which does exactly that?

<?php
print_r(
    array_filter(
        ["https", "www", "stackoverflow", "com"], 
        function($value) {
            return !in_array($value, ["https", "www", "com"]);
        }
    )
);

The output obviously is:

Array ( [2] => stackoverflow )

answered Nov 7, 2022 at 17:03

arkascha

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2 Comments

Nigel Ren Over a year ago

Would array_diff() be a better tool?

arkascha Over a year ago

@NigelRen Also an alternative, there is no yes or no for that. It depends on the actual task the OP faces. The code in the OPs question obviously is just a demonstration, not the real task. array_filter() offers much more flexibility. Just think of case insensivity and trimming for example.

Salvino D'sa · Accepted Answer · 2022-11-07 17:10:27Z

0

Think I might be late, but this is happening because you were modifying the original array. A much more cleaner way of doing this would be as follows:

<?php

$search_array = array("https", "www", "stackoverflow", "com");

for ($i=count($search_array)-1; $i>=0; $i--) { 
    if ( in_array(strtolower($search_array[$i]), ["https", "www", "com"]) )
        unset($search_array[$i]);
}

echo print_r($search_array, true);

answered Nov 7, 2022 at 17:10

Salvino D'sa

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