Default array values if key doesn't exist?

I know this is an old question, but my Google search for "php array default values" took me here, and I thought I would post the solution I was looking for, chances are it might help someone else.

I wanted an array with default option values that could be overridden by custom values. I ended up using array_merge.

Example:

<?php
    $defaultOptions = array("color" => "red", "size" => 5, "text" => "Default text");
    $customOptions = array("color" => "blue", "text" => "Custom text");
    $options = array_merge($defaultOptions, $customOptions);
    print_r($options);
?>

Outputs:

Array
(
    [color] => blue
    [size] => 5
    [text] => Custom text
)

As of PHP 7, there is a new operator specifically designed for these cases, called Null Coalesce Operator.

So now you can do:

echo $items['four']['a'] ?? 99;

instead of

echo isset($items['four']['a']) ? $items['four']['a'] : 99;

There is another way to do this prior the PHP 7:

function get(&$value, $default = null)
{
    return isset($value) ? $value : $default;
}

And the following will work without an issue:

echo get($item['four']['a'], 99);
echo get($item['five'], ['a' => 1]);

But note, that using this way, calling an array property on a non-array value, will throw an error. E.g.

echo get($item['one']['a']['b'], 99);
// Throws: PHP warning:  Cannot use a scalar value as an array on line 1

Also, there is a case where a fatal error will be thrown:

$a = "a";
echo get($a[0], "b");
// Throws: PHP Fatal error:  Only variables can be passed by reference

At final, there is an ugly workaround, but works almost well (issues in some cases as described below):

function get($value, $default = null)
{
    return isset($value) ? $value : $default;
}
$a = [
    'a' => 'b',
    'b' => 2
];
echo get(@$a['a'], 'c');      // prints 'c'  -- OK
echo get(@$a['c'], 'd');      // prints 'd'  -- OK
echo get(@$a['a'][0], 'c');   // prints 'b'  -- OK (but also maybe wrong - it depends)
echo get(@$a['a'][1], 'c');   // prints NULL -- NOT OK
echo get(@$a['a']['f'], 'c'); // prints 'b'  -- NOT OK
echo get(@$a['c'], 'd');      // prints 'd'  -- OK
echo get(@$a['c']['a'], 'd'); // prints 'd'  -- OK
echo get(@$a['b'][0], 'c');   // prints 'c'  -- OK
echo get(@$a['b']['f'], 'c'); // prints 'c'  -- OK
echo get(@$b, 'c');           // prints 'c'  -- OK

This should do the trick:

$value =  isset($items['four']['a']) ? $items['four']['a'] : 99;

A helper function would be useful, if you have to write these a lot:

function arr_get($array, $key, $default = null){
    return isset($array[$key]) ? $array[$key] : $default;
}

As of PHP7.0

You may use the null coalescing operator: ??

$value = $items['four']['a'] ?? 99;
echo $value;

# or simply
echo $items['four']['a'] ?? 99;

As of PHP7.4

You could instead use the null coalescing assignment operator if you want to additionally assign the default value to the array key if empty.

$items['four']['a'] ??= 99;
echo $items['four']['a'];

For PHP <=5.x

If you can guarantee that 'four' and 'a' keys always exist and is either a truthy or falsy value, then you may use the ternary operator with empty middle part: ?:

However, if the array keys are not guaranteed to exist, this may give you errors, so be careful to check with isset() or !empty() (see the long-form answer below).

$value = $items['four']['a'] ?: 99;
echo $value;

All versions of PHP support the long-form ternary operator:

$value = !empty($items['four']['a']) ? $items['four']['a'] : 99;
echo $value;

Note that this does not return 99 if and only if the key 'a' is not set in items['four']. Instead, it returns 99 if and only if the value $items['four']['a'] is either unset or a falsy value value like an empty string (''), empty array, NULL, 0, or FALSE.

The question is very old, but maybe my solution is still helpful. For projects where I need "if array_key_exists" very often, such as Json parsing, I have developed the following function:

function getArrayVal($arr, $path=null, $default=null) {
    if(is_null($path)) return $arr;
    $t=&$arr;
    foreach(explode('/', trim($path,'/')) As $p) {
        if(!array_key_exists($p,$t)) return $default;
        $t=&$t[$p];
    }
    return $t;
}

You can then simply "query" the array like:

$res = getArrayVal($myArray,'companies/128/address/street');

This is easier to read than the equivalent old fashioned way...

$res = (isset($myArray['companies'][128]['address']['street']) ? $myArray['companies'][128]['address']['street'] : null);

Not that I know of.

You'd have to check separately with isset

echo isset($items['four']['a']) ? $items['four']['a'] : 99;

Use Array_Fill() function

http://php.net/manual/en/function.array-fill.php

$default = array(
              'a' => 1,
              'b' => 2,
              'c' => 3,
              'd' => 4,
         );
$arr = Array_Fill(1,3,$default);
print_r($arr);

This is the result:

Array
(
    [1] => Array
        (
            [a] => 1
            [b] => 2
            [c] => 3
            [d] => 4
        )

    [2] => Array
        (
            [a] => 1
            [b] => 2
            [c] => 3
            [d] => 4
        )

    [3] => Array
        (
            [a] => 1
            [b] => 2
            [c] => 3
            [d] => 4
        )

)

I don't know of a way to do it precisely with the code you provided, but you could work around it with a function that accepts any number of arguments and returns the parameter you're looking for or the default.

Usage:

echo arr_value($items, 'four', 'a');

or:

echo arr_value($items, 'four', 'a', '1', '5');

Function:

function arr_value($arr, $dimension1, $dimension2, ...)
{
    $default_value = 99;
    if (func_num_args() > 1)
    {
        $output = $arr;
        $args = func_gets_args();
        for($i = 1; $i < func_num_args(); $i++)
        {
            $outout = isset($output[$args[$i]]) ? $output[$args[$i]] : $default_value;
        }
    }
    else
    {
        return $default_value;
    }

    return $output;
}

You can use DefaultArray from Non-standard PHP library. You can create new DefaultArray from your items:

use function \nspl\ds\defaultarray;
$items = defaultarray(function() { return defaultarray(99); }, $items);

Or return DefaultArray from the items() function:

function items() {
    return defaultarray(function() { return defaultarray(99); }, array(
        'one' => array(
              'a' => 1,
              'b' => 2,
              'c' => 3,
              'd' => 4,
         ),
         'two' => array(
              'a' => 1,
              'b' => 2,
              'c' => 3,
              'd' => 4,
         ),
         'three' => array(
              'a' => 1,
              'b' => 2,
              'c' => 3,
              'd' => 4,
         ),
    ));
}

Note that we create nested default array with an anonymous function function() { return defaultarray(99); }. Otherwise, the same instance of default array object will be shared across all parent array fields.

Currently using of php 7.2

>>> $a = ["cat_name"=>"Beverage", "details"=>"coca cola"];
=> [
     "cat_name" => "Beverage",
     "details" => "coca cola",
   ]
>>> $a['price']
PHP Notice:  Undefined index: price in Psy Shell code on line 1
=> null
>>> $a['price'] ?? null ? "It has price key" : "It does not have price key"
=> "It does not have price key"

In PHP7, as Slavik mentioned, you can use the null coalescing operator: ??

Link to the PHP docs.