up vote 10 down vote favorite
6

I have an array such as:

Array
(
[0] => Array
    (
        [id] => 2
        [type] => comment
        [text] => hey
        [datetime] => 2010-05-15 11:29:45
    )

[1] => Array
    (
        [id] => 3
        [type] => status
        [text] => oi
        [datetime] => 2010-05-26 15:59:53
    )

[2] => Array
    (
        [id] => 4
        [type] => status
        [text] => yeww
        [datetime] => 2010-05-26 16:04:24
    )

)

Can anyone suggest a way to sort/order this based on the datetime element?

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2 Answers

up vote 23 down vote accepted

Use usort() and a custom comparison function:

function date_compare($a, $b)
{
    $t1 = strtotime($a['datetime']);
    $t2 = strtotime($b['datetime']);
    return $t1 - $t2;
}    
usort($array, 'date_compare');

EDIT: Your data is organized in an array of arrays. To better distinguish those, let's call the inner arrays (data) records, so that your data really is an array of records.

usort will pass two of these records to the given comparison function date_compare() at a a time. date_compare then extracts the "datetime" field of each record as a UNIX timestamp (an integer), and returns the difference, so that the result will be 0 if both dates are equal, a positive number if the first one ($a) is larger or a negative value if the second argument ($b) is larger. usort() uses this information to sort the array.

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in this example, does $array need to contain elements $a and $b? - im getting an error invalid compare function – Tim May 26 '10 at 6:52
Nope, $a and $b will hold the arrays within $array. Make sure that you did not misspell the function name. – Ferdinand Beyer May 26 '10 at 6:57
im not sure I understand. In my example, I have 3 arrays in the array - I have confirmed the name, still getting invalid comparison function – Tim May 26 '10 at 7:01
See the explanation I added. I tested the code and it works fine for me! – Ferdinand Beyer May 26 '10 at 7:11
2  
I don't know CodeIgniter, but are you defining the function inside a class? Than you either have to define it outside the class or use a different callback argument: usort($array, array($this, "date_compare")), so that usort() knows it's a class function/method. See also: php.net/manual/en/… – Ferdinand Beyer May 26 '10 at 16:26
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up vote 0 down vote

http://us2.php.net/manual/en/function.array-multisort.php see third example:

<?php

$data[] = array('volume' => 67, 'edition' => 2);
$data[] = array('volume' => 86, 'edition' => 1);
$data[] = array('volume' => 85, 'edition' => 6);
$data[] = array('volume' => 98, 'edition' => 2);
$data[] = array('volume' => 86, 'edition' => 6);
$data[] = array('volume' => 67, 'edition' => 7);

foreach ($data as $key => $row) {
    $volume[$key]  = $row['volume'];
    $edition[$key] = $row['edition'];
}

array_multisort($volume, SORT_DESC, $edition, SORT_ASC, $data);

?>

fyi, using a unix (seconds from 1970) or mysql timestamp (YmdHis - 20100526014500) would be be easier for the parser but i think in your case it makes no difference.

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