How to check if multiple array keys exists

If you only have 2 keys to check (like in the original question), it's probably easy enough to just call array_key_exists() twice to check if the keys exists.

if (array_key_exists("story", $arr) && array_key_exists("message", $arr)) {
    // Both keys exist.
}

However this obviously doesn't scale up well to many keys. In that situation a custom function would help.

function array_keys_exists(array $keys, array $arr) {
   return !array_diff_key(array_flip($keys), $arr);
}

Surprisingly array_keys_exist doesn't exist?! In the interim that leaves some space to figure out a single line expression for this common task. I'm thinking of a shell script or another small program.

Note: each of the following solutions use concise […] array declaration syntax available in php 5.4+

array_diff + array_keys

if (0 === count(array_diff(['story', 'message', '…'], array_keys($source)))) {
  // all keys found
} else {
  // not all
}

(hat tip to Kim Stacks)

This approach is the most brief I've found. array_diff() returns an array of items present in argument 1 not present in argument2. Therefore an empty array indicates all keys were found. In php 5.5 you could simplify 0 === count(…) to be simply empty(…).

array_reduce + unset

if (0 === count(array_reduce(array_keys($source), 
    function($in, $key){ unset($in[array_search($key, $in)]); return $in; }, 
    ['story', 'message', '…'])))
{
  // all keys found
} else {
  // not all
}

Harder to read, easy to change. array_reduce() uses a callback to iterate over an array to arrive at a value. By feeding the keys we're interested in the $initial value of $in and then removing keys found in source we can expect to end with 0 elements if all keys were found.

The construction is easy to modify since the keys we're interested in fit nicely on the bottom line.

array_filter & in_array

if (2 === count(array_filter(array_keys($source), function($key) { 
        return in_array($key, ['story', 'message']); }
    )))
{
  // all keys found
} else {
  // not all
}

Simpler to write than the array_reduce solution but slightly tricker to edit. array_filter is also an iterative callback that allows you to create a filtered array by returning true (copy item to new array) or false (don't copy) in the callback. The gotchya is that you must change 2 to the number of items you expect.

This can be made more durable but verge's on preposterous readability:

$find = ['story', 'message'];
if (count($find) === count(array_filter(array_keys($source), function($key) use ($find) { return in_array($key, $find); })))
{
  // all keys found
} else {
  // not all
}

Here is a solution that's scalable, even if you want to check for a large number of keys:

<?php

// The values in this arrays contains the names of the indexes (keys) 
// that should exist in the data array
$required = array('key1', 'key2', 'key3');

$data = array(
    'key1' => 10,
    'key2' => 20,
    'key3' => 30,
    'key4' => 40,
);

if (count(array_intersect_key(array_flip($required), $data)) === count($required)) {
    // All required keys exist!
}