sort array by use of GET variable.. no sorting

Question

I have an array consisting of 4 fields.

 $retval[] = array(
      "name" => "$dir$entry/",
      "type" => filetype("$dir$entry"),
      "size" => 0,
      "lastmod" => filemtime("$dir$entry")
    );

I want to sort this array depending on a variable, which contains either 1 of the 4 field (eg: type, name etc)

$sortBy = $_GET['sortBy'];

This function should use the $sortBy variable:

function compare_field($a, $b){
return strnatcmp($a["'.$sortBy.'"], $b["'.$sortBy.'"]) 
}

And is called like this:

usort($retval, "compare_field");

But the construction doesn't work ..

Hope someone can point me in the right direction, being the obvious newby I am.

Elias Van Ootegem · Accepted Answer · 2016-03-05 13:35:43Z

3

First, you're sorting by a key that is actually: '..', not the value of $sortBy. You're trying to use a variables value as the key, to do that, you don't need to mess around with quotes, just write $arrayName[$keyVariable]. That's it.
Second is that compare_field had no access to the $sortBy variable. That variable is local to the scope where it was created, or it's a global variable. Either way, functions don't have access to it.

If you want the usort callback to have access to the $sortBy variable, the easiest way would be to use a closure (anonymous function) as callback:

usort($retval, function ($a, $b) use ($sortBy) {
    return strnatcmp($a[$sortBy], $b[$sortBy]);
});

answered Mar 5, 2016 at 13:35

Elias Van Ootegem

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3 Comments

Sam Over a year ago

Interesting. Thanks for the input. I tried your solution, but $sortBy is still not used.If I replaceit by for instance "name" it works, but when I use $sortBy, nothing happens. and $sortBy does equal name ...

Sam Over a year ago

I got it to work using the old code, but indeed without the quotes, and by making $sortBy global. Something of a scope issue like you pointed out .. but apparently your solution still has that scope issue? curious to what you think about it ..

Elias Van Ootegem Over a year ago

$sortBy needs to be available in the same scope as where you call usort. You can't pass $sortBy to the anonymous function unless the place where you declare that function has access to this variable. If you're calling usort in a scope other than the global one (ie a function, or a method), then that's why it's not working. I'd need to see more code to tell for sure

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