array_key_exists($key, $array) vs !empty($array[$key])

Question

I've seen a lot of people do the former, is there any performance benefit doing one vs the other? Or is it just an eye candy? I personally use the latter every time as it is shorter and personally more readable to me.

Answer 1

The other responses focus on the differences between the two functions. This is true, but if the source array does not contain null or 0 or "", ... (empty values) values you can benchmark the speed of the two functions:

<?php

function makeRandomArray( $length ) {
    $array = array();
    for ($i = 0; $i < $length; $i++) {
        $array[$i] = rand(1, $length);
    }

    return $array;
}

function benchmark( $count, $function ) {
    $start = microtime(true);
    for ($i = 0; $i < $count; $i++) {
        $function();
    }
    return microtime(true) - $start;
}

$runs = 100000;
$smallLength = 10;
$small = makeRandomArray($smallLength);

var_dump(benchmark($runs, function() {
    global $small, $smallLength;
    array_key_exists(rand(0, $smallLength), $small);
}));
var_dump(benchmark($runs, function() {
    global $small, $smallLength;
    !empty($small[rand(0, $smallLength)]);
}));

Which gave me the following results:

For a small array:

• array_key_exists: float(0.18357992172241)
• empty: float(0.072798013687134)
• isset: float(0.070242881774902)

For a relative big array:

• array_key_exists: float(0.57489585876465)
• empty: float(0.0068421363830566)
• isset: float(0.0069410800933838)

So if it's possible it's faster to use empty or isset.

Answer 2

array_key_exists($key, $array) and !empty($array[$key]) can produce different results therefore it is not a matter of performance or preference.

                              | array_key_exists($key, $array) | !empty($array[$key]) |
+-----------------------------+--------------------------------|----------------------+
| $array[$key] does not exist | false                          | false                |
| $array[$key] is truthy      | true                           | true                 |
| $array[$key] is falsey      | true                           | false                |

You can see that the truth table is different for falsey values (false, 0, NULL, etc). Therefore !empty($array[$key]) is not suitable in situations where a falsey value could be considered present e.g. $array["number_of_children"] should not be tested for emptiness where the value 0 makes sense.

---

You can use isset($array[$key]) which produces results identical to array_key_exists($key, $array) with exactly one exception:

                                      | array_key_exists($key, $array) | isset($array[$key]) |
+-------------------------------------+--------------------------------|---------------------+
| $array[$key] does not exist         | false                          | false               |
| $array[$key] is truthy              | true                           | true                |
| $array[$key] is falsey but not NULL | true                           | true                |
| $array[$key] is NULL                | true                           | false               |