Using a for() loop after array_filter() gives Warning: Undefined array key [duplicate]

Question

I'm using array_filter with multiple parameters but it's not doing the filter correctly. Here where it's supposed to return an array with only "arts,crafts,designs" as an element, it's returning an empty array. The only $askedcat parameter it works for is "arts". I can't find out what the issue is.

I've tried not using an array_filter and instead just looping over the array, and I get the same problem.

class CategoryFilter {
    public $categoryAskedFor;

    function __construct($askedCat) {
            $this->categoryAskedFor = $askedCat;
    }

    function categoryCallback($projectCategoryString) {
        $project_category_array = explode(",", $projectCategoryString);
        if(in_array($this->categoryAskedFor, $project_category_array)) return true;
        return false;
    }
}

$verifiedProjects = ["arts", "arts,crafts,designs", "film", "film,theater"];

$askedCat = "crafts";

$newArr = array_filter($verifiedProjects, array(new CategoryFilter($askedCat), "categoryCallback"));

for ($i = 0; $i < count($newArr); $i++) {
    echo $newArr[$i] . "<br>";
}

I expect the output here to be arts,crafts,design<br> but it's only <br> meaning the array is empty.

$this->categoryAskedFor instead of $this->$categoryAskedFor in __construct…!? — deceze
– deceze ♦, Commented Oct 28, 2019 at 15:21
What @deceze said plus the fact that you're looping over your array wrong. Use foreach (array_filter will preserve keys so the 0 index is not necessarily there after filtering). — Jeto
– Jeto, Commented Oct 28, 2019 at 15:22
Please go enable proper PHP error reporting. (Go read up on it, if you don’t know what that means.) PHP could alert you to a lot of these issues on its own already, before you need to go bother someone else with them. — 04FS
– 04FS, Commented Oct 28, 2019 at 15:23
Edited above @deceze wasn't my issue, just happened when I copied the code over here — bronkers
– bronkers, Commented Oct 28, 2019 at 15:23

Jayram Prajapati · Accepted Answer · 2019-10-28 15:39:54Z

There are many way to achieve this but let me show you two way here

WAY #1

If you using the for loop to retrieve the array value then need to have numeric key and as per your code you need array_values function to manage that

<?php

    class CategoryFilter {
        public $categoryAskedFor;

        function __construct($askedCat) {
                $this->categoryAskedFor = $askedCat;
        }

        function categoryCallback($projectCategoryString) {
            $project_category_array = explode(",", $projectCategoryString);
            if(in_array($this->categoryAskedFor, $project_category_array)) return true;
            return false;
        }
    }

    $verifiedProjects = ["arts", "arts,crafts,designs", "film", "film,theater"];

    $askedCat = "crafts";

    $newArr = array_filter($verifiedProjects, array(new CategoryFilter($askedCat), "categoryCallback"));

    $newArr = array_values($newArr);
    for ($i = 0; $i < count($newArr); $i++) {
        echo $newArr[$i] . "<br>";
    }

WAY # 2

If you don't want to use the array_values here then you need to manage the foreach loop instead of for loop

<?php

    class CategoryFilter {
        public $categoryAskedFor;

        function __construct($askedCat) {
                $this->categoryAskedFor = $askedCat;
        }

        function categoryCallback($projectCategoryString) {
            $project_category_array = explode(",", $projectCategoryString);
            if(in_array($this->categoryAskedFor, $project_category_array)) return true;
            return false;
        }
    }

    $verifiedProjects = ["arts", "arts,crafts,designs", "film", "film,theater"];

    $askedCat = "crafts";

    $newArr = array_filter($verifiedProjects, array(new CategoryFilter($askedCat), "categoryCallback"));

    foreach ($newArr as $value) {
        echo $value . "<br>";
    }

Jeto · Accepted Answer · 2019-10-28 15:29:21Z

0

The way you're looping over your resulting array is wrong, because array_filter will preserve the array keys. The 0 index may not be there in the filtered version (and in your case, it actually isn't).

Use foreach instead:

foreach ($newArr as $value) {
  echo $value, '<br>';
}

answered Oct 28, 2019 at 15:29

Jeto

15k2 gold badges39 silver badges50 bronze badges

3 Comments

Claudio Over a year ago

I think you meant echo $value . '<br>';

Jeto Over a year ago

@Claudio Nope, echo takes any number of parameters, this way you don't have to build/buffer a string before outputting it.

Claudio Over a year ago

Great, didn't knew that

rai · Accepted Answer · 2019-10-28 15:30:21Z

0

array_filter will remove elements but will not reset the keys. use array_values to reset the keys first.

$newArr = array_values($newArr);
for ($i = 0; $i < count($newArr); $i++) {
    echo $newArr[$i] . "<br>";
}

answered Oct 28, 2019 at 15:30

rai

5194 silver badges11 bronze badges

1 Comment

bronkers Over a year ago

Thank you, while foreach solved the issue, this is very helpful!

Pravin Prajapati · Accepted Answer · 2019-10-29 08:20:45Z

0

You will get as per your output

$askedCat = 'crafts';
$verifiedProjects = ["arts", "arts,crafts,designs", "film", "film,theater"];
$newArr = array_filter($verifiedProjects, function ($item) use ($askedCat) {
    if (stripos($item, $askedCat) !== false) {
        return true;
    }
    return false;
});

foreach ($newArr as $value) {
        echo $value . "<br>";
    }

edited Oct 29, 2019 at 8:20

answered Oct 28, 2019 at 16:07

Pravin Prajapati

504 bronze badges

Collectives™ on Stack Overflow

Using a for() loop after array_filter() gives Warning: Undefined array key [duplicate]

4 Answers 4

Comments

3 Comments

1 Comment

Comments

Linked

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

Comments

3 Comments

1 Comment

Comments

Linked

Related