PHP-以递归方式将字符串替换为数字花费的时间太长 [英] PHP - Recursive in place replacing of strings to numbers takes too long

问题描述

因为MYSQL的"SELECT"选择整数并将其作为字符串进行浮点运算，所以我需要从JS中获得的每个响应都必须位于正确的数据模型中-

Because MYSQL's "SELECT" selects integers and floats as strings, and I need every response I get (from JS) to be in a correct data model -

• 1个不是"1"，
• 53.2不是"53.2"，

我创建了适用于混合类型-数组/对象的递归函数:

I created this recursive function that works on mixed type - array/object:

private function cast_number(&$mixed) {
    if(is_array($mixed)) {
        foreach ($mixed as $key => $val)
            if (is_numeric($val))
                $mixed[$key] = (double)$val;
            else if (is_array($val) || is_object($val))
                $mixed[$key] = $this->cast_number($val);
    } else if(is_object($mixed)) {
        foreach ($mixed as $key => $val)
            if (is_numeric($val))
                $mixed->$key = (double)$val;
            else if (is_array($val) || is_object($val))
                $mixed->$key = $this->cast_number($val);
    }
    return $mixed;
}

非常简单的功能-如果为数字，则转换为双精度，如果为数组或对象，则递归遍历.

Pretty simple function - if is number, cast double, if is array or object, go over recursivly.

这里的一切都准备就绪.

Everything here is in place.

我对此有两个问题: -在6MB的数据上，大多数数字以字符串表示，耗时0.5秒 -在200MB的数据上(是的，我需要它，请不要专注于它)，它在几分钟(通常是几秒钟)后失败，表示需要4GB以上的内存.

I have two problems with this: - On 6MB of data, of mostly numbers that are represented as strings it took 0.5 seconds - On 200MB of data (yes, I need it, please don't focus on it), it failed after a couple of minutes (usually seconds), saying it needs more than 4GB of memory..

1. 如何改善此功能? (速度，内存)
2. 为什么要花这么长时间?甚至json_encode，我认为这是一个更大的函数也需要更少的时间..

推荐答案

由于强制以前比强制转换快，我运行了这段代码来计算PHP 7上的计时:

Because coercion used to be faster than casting, I ran this code to calculate timings on PHP 7 :

function getTime($start) {
    return round((microtime(true) - $start) * 1000000) / 1000;
}

function mockData($length) {
    $data = [];
    $i = -1;

    while ($i++ < $length) {
        $data[$i] = strval(rand(1, 10000) / 100);
    }

    return $data;
}

$data = mockData(100000);

// Let's check that they are string before
echo gettype($data[0]) . '<br><br>';

$start = microtime(true);
$convertedData = [];
foreach ($data as $key => $value) {
    $convertedData[$key] = (double) $value;
}
echo '(double) cast took ' . getTime($start) . ' ms.<br>';

$start = microtime(true);
$convertedData = [];
foreach ($data as $key => $value) {
    $convertedData[$key] = 0 + $value;
}
echo 'Coercion took ' . getTime($start) . ' ms.<br>';

我的结果是:

(double) cast took 27.508 ms.
Coercion took 28.789 ms.

结论

由于使用floatval(实现字符串到双精度转换的第三种方法)的时间更长，因此使用PHP不能做得更好.您要实现的是脚本操作，不应将其用作Web应用程序的常规后端操作.

Since using floatval (a third way to achieve string to double conversion) is even longer, you can't do better than that with PHP. What you're trying to achieve is a scripting operation, it shouldn't be used as a normal back-end operation for a web application.

但是，如果您仍然希望这样做，则可以在php.ini文件不要使用-1解决方法.

But if you still want to do that, you can higher your memory_limit inside your php.ini file, as long as you don't use the -1 workaround.

更新

我忘记了一种可能的优化方法，您应该通过引用传递变量至少执行立即分配:

I forgot one possible optimization, you should pass your variable by reference to at least execute immediate assignation :

$start = microtime(true);
foreach ($data as $key => $value) {
    $data[$key] = (double) $value;
}
echo getTime($start) . ' ms.<br>';

=> 34.018毫秒.

$start = microtime(true);
foreach ($data as &$value) {
    $value = (double) $value;
}
echo getTime($start) . ' ms.<br>';

=> 17.081毫秒.

显然，通过引用使用强制将产生更好的结果:

And apparently using coercion with by reference gives even better results :

$start = microtime(true);
foreach ($data as &$value) {
    $value = 0 + $value;
}
echo getTime($start) . ' ms.<br>';

=> 13.1毫秒.

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