PHP sorting by date

Question

I have tried to use usort but I am having issues

I have now used the usort function.

my array is has a string key and a string value which represents the date

my output is as follows:

It is only sorting by the first two numbers, I want it to sort for the full date, What am I doing wrong?

This is my code:

usort($filesWithDates,"my_sort");
foreach ($filesWithDates as &$value) {
    echo $value."<br/>";
}

function my_sort($a,$b)
{
if ($a==$b) return 0;
return ($a<$b)?-1:1;
}
foreach ($filesWithDates as &$value) {
        echo $value."<br/>";
    }

You can avoid many issues if you use ISO format for dates (YYYY-mm-dd) or simple unix timestamps. Other than that, you have to parse/explode $a and $b in your compare function, not just compare the string. — ToBe
– ToBe, Commented Mar 4, 2014 at 15:20

John Conde · Accepted Answer · 2014-03-04 15:19:58Z

4

Those aren't dates. Those are strings. You need to put your dates into a proper format that is either sortable as strings or compare them as dates using DateTime():

usort($filesWithDates, function($a, $b) {
    $date1 = DateTime::createFromFormat('d/m/Y', $a);
    $date2 = DateTime::createFromFormat('d/m/Y', $b);
    return $date1 > $date2;
});
foreach ($filesWithDates as $value) {
    echo $value."<br/>";
}

answered Mar 4, 2014 at 15:19

John Conde

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5 Comments

ex3v Over a year ago

Didn't know usort takes callable as parameter. Nice!

Joe Over a year ago

I have one problem, before i call this function, my key value is a string, after this function is executed, my array keys have been changed to '0, 1, 2, 3, 4....' etc. Why would it override my key ?

John Conde Over a year ago

From the manual:

Note: This function assigns new keys to the elements in array. It will remove any existing keys that may have been assigned, rather than just reordering the keys.

So if you want to preserve keys just copy the array to a new variable first and then sort that array.

Joe Over a year ago

Okay, but how I would I then re-match the keys with the reordered dateS?

John Conde Over a year ago

Try changing usort to uasort

Styphon · Accepted Answer · 2014-03-04 15:20:16Z

0

Convert your dates to integers first:

$datesAsInts = array();
foreach($filesWithDats as $value) {
    $datesAsInts[] = strtotime($value);
}
usort($datesAsInts,"my_sort");
foreach ($datesAsInts as $value) {
    echo date('d/m/Y', $value)."<br/>";
}

function my_sort($a,$b)
{
    if ($a==$b) return 0;
    return ($a<$b)?-1:1;
}

answered Mar 4, 2014 at 15:20

Styphon

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5 Comments

ToBe Over a year ago

This still does not parse the dates and sort them correctly

Styphon Over a year ago

@ToBe How about giving someone time to write their answer... When you down voted it was an exact copy of his code.

ToBe Over a year ago

Ok, granted. But why post the answer if it wasnt finished? Anyways. Not the place to debate this. I'll remove my downvote when the answer changes. (Down removed)

Styphon Over a year ago

@ToBe Why? Because if you don't post half an answer and then edit it these days then someone else will have pipped you to it. And even then half the time someone will still beat you to it.

ToBe Over a year ago

Youre right, that happens a lot. Still I couldnt guess youre still editing. But dont worry, neg has been removed. So no need to chat about it anymore.

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