Sort array by date - php

Question

My array has an array for each field (i.e date, name, etc.). How do I sort the array by date? Should I create another array? Can I use sort or unsort here. If yes, how? Here is my array:
Array
(
[date] => Array
(
[0] => 03/11/2019
[1] => 03/19/2019
[2] => 03/15/2019
[3] => 12/15/2018
)
[name] => Array
(
[0] => Lowa
[1] => Stephanie
[2] => Allan
[3] => Joffer
)
[number] => Array
(
[0] => 178989898
[1] => 111111111
[2] => 222222222
[3] => 333333333
)
[unit] => Array
(
[0] => HR
[1] => VPP
[2] =>
[3] => OAT
)
[department] => Array
(
[0] => Chemistry
[1] => IT
[2] => Lab
[3] => Contractor
)
)
At the end, my first element will be:
03/19/2019 Stephanie 111111111 VPP IT

Answer 1

I think your data can be better organized:
$newArr = Array
(
[0] => Array
(
[date] => 03/11/2019
[name] => Lowa
[number] => 178989898
[unit] => HR
[department] => Chemistry
)
[1] => Array
(
[date] => 03/19/2019
[name] => Stephanie
[number] => 111111111
[unit] => VPP
[department] => IT
)
[2] => Array
(
[date] => 03/15/2019
[name] => Allan
[number] => 222222222
[unit] =>
[department] => Lab
)
[3] => Array
(
[date] => 12/15/2018
[name] => Joffer
[number] => 333333333
[unit] => OAT
[department] => Contractor
)
);
Then, you can simply sort it by:
function cmp($a, $b) {
if ($a["date"] == $b["date"]) return 0;
return ($a["date"] < $b["date"]) ? -1 : 1;
}
usort($newArr, "cmp");
Please be warned that dates in the format "Month/Day/Year" ar not alphabetically sortable.
You definitively should use a Year/Month/Day format for your dates, or write a more specific cmp() function...
UPDATE: To answer OP's question in comment: just reverse $row and 'field' order:
for ($row = 0; $row < count($date); $row++) {
$newArr[$row]['date'] = $date[$row];
$newArr[$row]['name'] = $name[$row];
...
}

Answer 2

First save the keys of your array - then by using array_value convert to integer keys so you can use the ... operator.
Then you can use array_filter with null function to re-organize your array. Next step will be to get the keys back using array_map and array_combine.
Last step - sort by "data" with usort
Consider the following example:
$arr = ["date" => ["3", "7", "5"], "name" => ["aa", "bb", "cc"]]; // this can have a lot more sub-array inside
$keys = array_keys($arr); // extract the keys for later use
$res = array_map(null, ...array_values($arr)); // transposed the array
$res = array_map(function ($e) use ($keys) {return array_combine($keys, $e);}, $res); // return the keys to the transposed array
usort($res, function ($a, $b) {return strcmp($a['date'], $b['date']);} ); // sort all by "date"
Reference:
array-keys, array-filter, array-map, usort, array-values
Notice #MarcoS post comment regarding the comparing dates