Try to create basic function to sort array with usort

Question

I am trying to create a simple function to sort an array with usort and I don't understand what's wrong with my code.

For the test, I want to order by the field 'str' in "descending" order.

My array for the test :

$tabCustom = array(
    0 => array(
        'str' => 'cccc',
        'nb' => 1
    ),
    1 => array(
        'str' => 'aaaa',
        'nb' => 3
    ),
    2 => array(
        'str' => 'bbb',
        'nb' => 2
    )
);

Here the code who works well without custom function :

usort($tabCustom, function($a, $b)
{
    $order = 'desc';
    if($order == 'asc')
    {
        return strcasecmp($a['str'], $b['str']);
    }
    elseif($order == 'desc')
    {
        return strcasecmp($b['str'], $a['str']);
    }
});

The result :

Array
(
    [0] => Array
        (
            [str] => cccc
            [nb] => 1
        )

    [1] => Array
        (
            [str] => bbb
            [nb] => 2
        )

    [2] => Array
        (
            [str] => aaaa
            [nb] => 3
        )

)

And now I try to build a custom function based on the same code :

function arraySort($array, $field, $order = 'asc')
{
    usort($array, function($a, $b)
    {
        global $field;
        global $order;
        if($order == 'asc')
        {
            return strcasecmp($a[$field], $b[$field]);
        }
        elseif($order == 'desc')
        {
            return strcasecmp($b[$field], $a[$field]);
        }
    });
}
arraySort($tabCustom, 'str', 'desc');

The wrong result :

Array
(
    [0] => Array
        (
            [str] => cccc
            [nb] => 1
        )

    [1] => Array
        (
            [str] => bbb
            [nb] => 2
        )

    [2] => Array
        (
            [str] => aaaa
            [nb] => 3
        )

)

So I don't understand what's wrong, I have put the global variable for $field and $order because otherwise the code says Undefined variable, but my table sorting doesn't work.

Have you an idea about the problem?

Thanks :)

as a note (rather than solution): 9/10 globals should never be used, pass in parameters instead — treyBake
– treyBake, Commented Oct 11, 2019 at 10:14

Atural · Accepted Answer · 2019-10-11 10:33:22Z

2

Progrock is right - you have to use use here... The other problem is - if you define a custom function - you have to use a referenced array. Usort does it already automatically but you have to define it in your own function (the & operator is the magic key for situations like that).

The following should work:

function arraySort(&$array, $field, $order = 'asc')
{
    usort($array, function($a, $b) use ($field, $order)
    {
        return ($order == 'desc')   ?   strcasecmp($b[$field], $a[$field])  :   strcasecmp($a[$field], $b[$field]);
    });
}
arraySort($tabCustom, 'str', 'asc');

answered Oct 11, 2019 at 10:33

Atural

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2 Comments

Florian Richard Over a year ago

Thanks for you answer and for the script, I understand better my mistake now, and I doesn't know the usage of "use" and the "&" operator, if I understand the "&" permit to work on "$tabCustom" without use a "return $array" in my function like a copy ?

Atural Over a year ago

yeah something like that - there is a very well written point in the official documentation - take a look @ secure.php.net/manual/en/language.references.pass.php - and pls do me a favour - accept and upvote the answer of progrock or mine ... (this is how SO works if someone provides you with a solution)

Progrock · Accepted Answer · 2019-10-11 10:24:51Z

1

<?php

function a($foo) {
    b();
}

function b() {
    global $foo;
    var_dump($foo);
}

a('bar');

Output:

NULL

$foo is not in the global scope.

You can use 'use' to inherit variables from the parent scope:

usort($array, function($a, $b) use ($field, $order) {
  // Your code here.
});

answered Oct 11, 2019 at 10:24

Progrock

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3 Comments

Atural Over a year ago

the reference is also missig in his own function function arraySort(&array...

Progrock Over a year ago

@sintakonte good point! Without the reference, the sort occurs on a copy and the original array goes untouched.

Florian Richard Over a year ago

Thank you for your anwser, I doesn't know the usage of "use" for a function it's why I have try with "global", thanks

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