[英]Better way to count and construct unique array in PHP
我有以下代碼,需要花費很長時間才能執行。 有時它甚至會超時。
foreach ($totalownerships as $totalownership) {
if (!in_array($totalownership['titleno'], $totaltitles)) {
$result['totalowns'] += 1;
$totaltitles[] = $totalownership['titleno'];
$result['ownershipid'] = $result['ownershipid'] . " " .$totalownership['titleno'];
}
}
$totalownerships
數組大小為52225
。 是否有更好的方法來編寫此代碼,以便執行它需要很長時間?
這將快得多,使用PHP的快速內置數組操作工具來消除循環中的數組搜索:
// Add all titles to $totaltitles, for added speed
foreach ($totalownerships as $totalownership) {
$totaltitles[] = $totalownership['titleno'];
}
// For PHP 5.5+ you can use array_column() to get just the titleno field
//$totaltitles = array_column($totalownership, 'titleno');
// Use array_unique() to eliminate duplicate titles from $totaltitles
array_unique($totaltitles);
// Use count() to get a total count of $totaltitles
$result['totalowns'] = count($totaltitles);
// Use implode() for concatenation of title names
$result['ownershipid'] .= " " . implode(" ", $totaltitles);
有關更多PHP性能提示,請查看: PHP Bench
而不是使用O(n)
in_array操作,我會使用O(1)
鍵查找:
$totaltitles = array();
foreach ($totalownerships as $totalownership) {
if (!isset($totaltitles[$totalownership['titleno']])) {
$totaltitles[$totalownership['titleno']] = $totalownership['titleno'];
$result['ownershipid'] .= " " . $totalownership['titleno'];
}
}
$result['totalowns'] = count($totaltitles);
基本上,我們的想法是將您的唯一屬性用作數組鍵,這樣您就可以使用常量時間查找而不是線性查找。
如果你想采取(可能更慢)更漂亮的路線,你可以嘗試:
$uniques = array_unqiue(array_map(function($own) {
return $own['titleno'];
}, $totalownerships));
$result = array(
'ownershipid' => implode(' ', $uniques),
'totalowns' => count($uniques)
);
(正如Steven Moseley所說,如果您使用的是PHP 5.5,則可以使用array_column而不是該array_map調用。)
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