PHP - merge only keys of an array?

Question

Let's say I have a PHP array:

$array1 = array(
   'protein' => array('PROT', 100, 150),
   'fat'     => array('FAT',  100, 250),
   'carbs'   => arary('CARBS', 10, 20)
);

$array2 = array(
   'vitaminA' => array('vitA', 1, 2),
   'vitaminB' => array('vitB', 1, 2),
   'vitaminC' => arary('vitC', 1, 2)
);

Now I want a combined array of those nutrients (something like array_merge()), but I only need the keys, not the values themselves.

So either this:

$combined = array(
   'protein' => NULL,
   'fat'     => NULL,
   'carbs'   => NULL,
   'vitaminA'=> NULL,
   'vitaminB'=> NULL,
   'vitaminC'=> NULL
);

OR

$combined = array('protein', 'fat', 'carbs', 'vitaminA', 'vitaminB', 'vitaminC');

I can do this manually with a foreach loop, but I was hoping there's a function which would make this process fast and optimized.

array_merge(array_keys($array1),array_keys($array2))

rabudde
– rabudde

2013-06-27 17:31:08 +00:00
Commented Jun 27, 2013 at 17:31 — rabudde
– rabudde, Commented Jun 27, 2013 at 17:31

KilZone · Accepted Answer · 2013-06-27 17:47:59Z

2

Wouldn't this do the trick?

$combined = array_merge(array_keys($array1), array_keys($array2));

This would result in your option #2.

I haven't done any benchmarks but I know that isset() is faster than in_array() in many cases; something tells me that it will be the same for isset() versus array_key_exists(). If it matters that much, you could try to use this:

$combined = array_flip(array_merge(array_keys($array1), array_keys($array2)));

Which would result in something like this:

$combined = array(
    'protein' => 1,
    'fat'     => 2,
    'carbs'   => 3,
    'vitaminA'=> 4,
    'vitaminB'=> 5,
    'vitaminC'=> 6
);

That would allow you to use isset(), e.g. option #1.

#edit I did some research on the performance of all three mentioned functions and most, if not all, case studies show that isset() is the fastest of all (1, 2); mainly because it is not actually a function but a language construct.

However do note that we now use array_flip() to be able to use isset(), so we lose quite a few microseconds to flip the array; therefore the total execution time is only decreasing if (and only if) you use isset() quite often.

edited Jun 27, 2013 at 17:47

answered Jun 27, 2013 at 17:31

KilZone

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3 Comments

Frantisek Over a year ago

I'm wondering which is better -- keep them as keys (option 1) or values (option 2)? Which would be faster -- checking with isset(), or checking with array_key_exists(), or checking with in_array() ?

user428517 Over a year ago

@RichardRodriguez does performance matter that much in your app? we're talking minuscule differences here

KilZone Over a year ago

I'm not sure if the performance you gain by being able to use isset() is going to be enough to offset the use of array_flip(), but you can give it a shot. Both option #1 and option #2 can be created by simple PHP-functions.

J David Smith · Accepted Answer · 2013-06-27 17:34:33Z

0

This:

function array_merge_keys($arr1, $arr2) {
    return array_merge(array_keys($arr1), array_keys($arr2));
}

should do the trick.

answered Jun 27, 2013 at 17:34

J David Smith

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