php 排序时间戳数组

Question

我的 usort 结果出乎意料。

$ccpmail[] =  
    array(
            "mail_id"=>$evemailheader["mail_id"],
            "is_read"=>$evemailheader['is_read'],                                           
            "fromid"=>$evemailheader['from'],
            "fromname"=>$character_names[get_character_name($evemailheader['from'], $character_names)]['character_name'],
            "subject"=>$evemailheader['subject'],
            "labels"=>array("EVE Online"),
            'datestamp'=>strtotime($evemailheader['timestamp']),
            'date'=>$date
        );

$email[] =  
    array(
        "mail_id"=>$mailid,
        "is_read"=>$is_read,                                            
        "fromid"=>$message_parsed->getHeaderValue('from'),
        "fromname"=>$message_parsed->getHeader('from')->getPersonName(),
        "subject"=>$message_parsed->getHeaderValue('subject'),
        "labels"=>array("E-mail"),
        'datestamp'=>strtotime($message_parsed->getHeaderValue('date')),
        'date'=>$date->format('Y-m-d H:i:s')
    );


$allmail = array_merge($ccpmail, $email);

function sortByOrder($a, $b) {
return  $a['datestamp'] < $b['datestamp'];
}

usort($allmail, 'sortByOrder');
var_dump($allmail);

结果：

array(133) {
[0]=>
array(8) {
    ["mail_id"]=>
    string(32) "bcfc5f6b0365738e58c99e0501b37210"
    ["is_read"]=>
    bool(true)
    ["fromid"]=>
    string(22) "EMAIL"
    ["fromname"]=>
    string(12) "NAME"
    ["subject"]=>
    string(4) "tset"
    ["labels"]=>
    array(1) {
        [0]=>
        string(6) "E-mail"
    }
    ["datestamp"]=>
    int(1485509147)
    ["date"]=>
    string(19) "2017-01-27 09:25:47"
}
[1]=>
array(8) {
    ["mail_id"]=>
    string(32) "317c556f35213548598f0bb838a237c1"
    ["is_read"]=>
    bool(true)
    ["fromid"]=>
    string(22) "EMAIL"
    ["fromname"]=>
    string(12) "NAME"
    ["subject"]=>
    string(5) "etest"
    ["labels"]=>
    array(1) {
        [0]=>
        string(6) "E-mail"
    }
    ["datestamp"]=>
    int(1485509066)
    ["date"]=>
    string(19) "2017-01-27 09:24:26"
}
[2]=>
array(8) {
    ["mail_id"]=>
    int(364172046)
    ["is_read"]=>
    bool(false)
    ["fromid"]=>
    int(90766569)
    ["fromname"]=>
    string(13) "NAME"
    ["subject"]=>
    string(2) "hi"
    ["labels"]=>
    array(1) {
        [0]=>
        string(10) "EVE Online"
    }
    ["datestamp"]=>
    int(1485507000)
    ["date"]=>
    object(DateTime)#3 (3) {
        ["date"]=>
        string(26) "2017-01-27 08:50:00.000000"
        ["timezone_type"]=>
        int(2)
        ["timezone"]=>
        string(1) "Z"
    }
}
[3]=>
array(8) {
    ["mail_id"]=>
    int(364160956)
    ["is_read"]=>
    bool(true)
    ["fromid"]=>
    int(793110520)
    ["fromname"]=>
    string(10) "NAME"
    ["subject"]=>
    string(30) "theres no brakes on this train"
    ["labels"]=>
    array(1) {
        [0]=>
        string(10) "EVE Online"
    }
    ["datestamp"]=>
    int(1485455100)
    ["date"]=>
    object(DateTime)#7 (3) {
        ["date"]=>
        string(26) "2017-01-26 18:25:00.000000"
        ["timezone_type"]=>
        int(2)
        ["timezone"]=>
        string(1) "Z"
    }
}
[4]=>
array(8) {
    ["mail_id"]=>
    int(364160959)
    ["is_read"]=>
    bool(true)
    ["fromid"]=>
    int(793110520)
    ["fromname"]=>
    string(10) "NAME"
    ["subject"]=>
    string(10) "safe word?"
    ["labels"]=>
    array(1) {
        [0]=>
        string(10) "EVE Online"
    }
    ["datestamp"]=>
    int(1485455100)
    ["date"]=>
    object(DateTime)#5 (3) {
        ["date"]=>
        string(26) "2017-01-26 18:25:00.000000"
        ["timezone_type"]=>
        int(2)
        ["timezone"]=>
        string(1) "Z"
    }
}
[5]=>
array(8) {
    ["mail_id"]=>
    int(364160957)
    ["is_read"]=>
    bool(true)
    ["fromid"]=>
    int(1228369447)
    ["fromname"]=>
    string(7) "NAME"
    ["subject"]=>
    string(4) "spam"
    ["labels"]=>
    array(1) {
        [0]=>
        string(10) "EVE Online"
    }
    ["datestamp"]=>
    int(1485455100)
    ["date"]=>
    object(DateTime)#6 (3) {
        ["date"]=>
        string(26) "2017-01-26 18:25:00.000000"
        ["timezone_type"]=>
        int(2)
        ["timezone"]=>
        string(1) "Z"
    }
}
[6]=>
array(8) {
    ["mail_id"]=>
    int(364160934)
    ["is_read"]=>
    bool(true)
    ["fromid"]=>
    int(94312752)
    ["fromname"]=>
    string(19) "NAME"
    ["subject"]=>
    string(4) "spam"
    ["labels"]=>
    array(1) {
        [0]=>
        string(10) "EVE Online"
    }
    ["datestamp"]=>
    int(1485455040)
    ["date"]=>
    object(DateTime)#11 (3) {
        ["date"]=>
        string(26) "2017-01-26 18:24:00.000000"
        ["timezone_type"]=>
        int(2)
        ["timezone"]=>
        string(1) "Z"
    }
}

如您所见，数组没有按照我想要的方式排序。我想要最低的时间戳在顶部。谁能帮帮我？

Answer 1

您的比较函数需要 return 一个大于、小于或等于零的整数才能正确排序。 (See the definition of value_compare_func here.) 这个表达式：

return  $a['datestamp'] < $b['datestamp'];

只会 return true 或 false （1 或 0，）这两个都不是将较早的时间戳排在较晚的时间戳之前的正确值 (-1)。

您可以再添加一项比较，以便它获得正确排序所需的值。

function sortByOrder($a, $b) {
    if ($a['datestamp'] < $b['datestamp']) return -1;    // return -1 if $a is earlier
    return  $a['datestamp'] > $b['datestamp'];    // return 1 if $a is later, or 0 if equal
}

如另一个答案所述，如果您使用的是 PHP 7，则有一个运算符 (<=>) 可以让您用一条语句完成此操作。

Answer 2

如果您使用 PHP7 或更高版本，您可以使用 spaceship 运算符，如下所示：

function sortByOrder($a, $b) {
    return  $a['datestamp'] <=> $b['datestamp'];
}

这将按照您的需要对其进行排序。如果不使用 PHP7 或更高，则必须进行一些 if 语句以查看它是更高、更低还是等于。

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