Geek asks and answers

What is the fastest? Conditions inside the loop or outside?

What is the fastest? To fulfill a condition based on a variable outside the loop inside the loop or outside, or does it even matter (does the compiler do this for you), or can you use a completely different workaround?

Example # 1 with a condition inside a loop (one foreach):

$test = 2;  
foreach ($list as $listItem) {
    if ($test == 1) {
        $listItem .= " - one";
    } else if ($test == 2) {
        $listItem .= " - two";
    } else if ($test == 3) {
        $listItem .= " - three";
    }
}

Example # 2 with an off-loop condition (pretty ugly with multiple foreach's):

$test = 2;  
if ($test == 1) {
    foreach ($list as $listItem) {
        $listItem .= " - one";
    }
} else if ($test == 2) {
    foreach ($list as $listItem) {
        $listItem .= " - two";
    }
} else if ($test == 3) {
    foreach ($list as $listItem) {
        $listItem .= " - three";
    }
}
+5
source share
2 answers

As you probably might have guessed, example 2 is faster, and the compiler does not do this for you.

Overview

condition inside or outside loop graph

Performance tests

Example # 1, a condition inside a loop:

Time taken: 0.2501 seconds
Time taken: 0.2336 seconds
Time taken: 0.2335 seconds
Time taken: 0.2319 seconds
Time taken: 0.2337 seconds 
Average:    0.2364 seconds

And the code:

<?php
    $list = array();
    for ($i = 0; $i < 1000000; $i++) {
        $list[] = md5(rand(0, 100000) * $i);
    }
    $a = microtime(true);
    $test = 2;
    foreach ($list as $listItem) {
        if ($test == 1) {
            $listItem .= " - one";
        } else if ($test == 2) {
            $listItem .= " - two";
        } else if ($test == 3) {
            $listItem .= " - three";
        }
    }
    echo "Time taken: " . number_format(microtime(true) - $a, 4) . " seconds";
?>

Example # 2, a condition outside the loop:

Time taken: 0.1424 seconds
Time taken: 0.1426 seconds
Time taken: 0.1364 seconds
Time taken: 0.1348 seconds
Time taken: 0.1347 seconds
Average:    0.1382 seconds

And the code:

<?php
    $list = array();
    for ($i = 0; $i < 1000000; $i++) {
        $list[] = md5(rand(0, 100000) * $i);
    }
    $a = microtime(true);
    $test = 2;
    if ($test == 1) {
        foreach ($list as $listItem) {
            $listItem .= " - one";
        }
    } else if ($test == 2) {
        foreach ($list as $listItem) {
            $listItem .= " - two";
        }
    } else if ($test == 3) {
        foreach ($list as $listItem) {
            $listItem .= " - three";
        }
    }
    echo "Time taken: " . number_format(microtime(true) - $a, 4) . " seconds";
?>

, , , , int?

# 3, , :

Time taken: 0.1845 seconds
Time taken: 0.1821 seconds
Time taken: 0.1745 seconds
Time taken: 0.1777 seconds
Time taken: 0.1767 seconds
Average:    0.1791 seconds

:

<?php
    $list = array();
    for ($i = 0; $i < 1000000; $i++) {
        $list[] = md5(rand(0, 100000) * $i);
    }
    $a = microtime(true);
    $test = 2;
    $result1 = ($test == 1);
    $result2 = ($test == 2);
    $result3 = ($test == 3);
    foreach ($list as $listItem) {
        if ($result1) {
            $listItem .= " - one";
        } else if ($result2) {
            $listItem .= " - two";
        } else if ($result3) {
            $listItem .= " - three";
        }
    }
    echo "Time taken: " . number_format(microtime(true) - $a, 4) . " seconds";
?>

. , , ​​ array_walk?

# 4, array_walk:

Time taken: 0.4950 seconds
Time taken: 0.4946 seconds
Time taken: 0.4947 seconds
Time taken: 0.4937 seconds
Time taken: 0.4918 seconds
Average:    0.4940 seconds

:

<?php
    function append_string($value, $suffix) {
        return $value . $suffix;
    }

    $list = array();
    for ($i = 0; $i < 1000000; $i++) {
        $list[] = md5(rand(0, 100000) * $i);
    }
    $a = microtime(true);
    $test = 2;
    if ($test == 1) {
        array_walk($list, "append_string", " - one");
    } else if ($test == 2) {
        array_walk($list, "append_string", " - two");
    } else if ($test == 3) {
        array_walk($list, "append_string", " - three");
    }
    echo "Time taken: " . number_format(microtime(true) - $a, 4) . " seconds";
?>

?! , C ++, , , .

/

# 1

  • ( , )

# 1

  • ( 71% , # 2 32% , # 3)

# 2

# 2

  • , ( , )

# 3

  • , # 1
  • , # 1

# 3

  • , # 2 ( 30%)

# 4

# 4

  • ( 100% ( № 1)). , - , 1,000,000 .
  • global .

PHP , , , , # 2, . , , # 1 # 3. , , , # 4.

+9

, . ( - , , , ).

, , . array_map. :

function append_str($value, $suffix) {
    return $value . $suffix;
}

if ($test == 1)
    array_map("append_str", $list, " - one");
else if ($test == 2)
    array_map("append_str", $list, " - two");
else if ($test == 3)
    array_map("append_str", $list, " - three");

. , , (append_str) , .

: , array_map, , C/++, , PHP ( Perl map).

+1

More articles:


All Articles